Funeral arrangements are pending, according to Franzen-Davis Funeral Home and Crematory in Livingston, Montana.
In 2016, Kidder told entertainment website Hey U Guys that her chemistry with Reeve was authentic "because we came from similar backgrounds and he looked like one of my brothers".
Although she's best known for playing the tough-as-nails journalist Lois Lane, Kidder struggled with mental illness over the years, and has spoken publicly about the battle with manic depression she waged both before and after she suffered a nervous breakdown in 1996.
She was unable to work for two years after serious vehicle crash in 1990. "These are hard words to write, so simply - you will be so very missed, my dear Margot". Her first major feature was Gaily, Gaily with Beau Bridges. She also made appearances in The Amityville Horror, Black Christmas and the TV series Boston Common.
Following her graduation, she joined the Canadian Broadcasting Corporation and started to find work on the small screen before moving to films with Gaily Gaily and Quackser Fortune Has A Cousin In The Bronx. And, after watching Kidder, you will believe Lois backs down from no one.
Margot Kidder Dead: 'Superman' Star Dies at 69
Marvel Studios President Kevin Feige called the moment "the best cinematic superhero save in the history of film" at an Academy of Motion Picture Arts and Sciences event honouring Donner a year ago.
The late actress rose to fame in 1978 for her portrayal of journalist and Superman's love interest, Lois Lane, opposite Christopher Reeve.
This was later reported as the reason she appeared in less than five minutes of Superman III four years later. Kidder recalled her childhood in northern Canada, saying, "We didn't have movies in this little mining town".
She is survived by her daughter.
The star also dated former Canadian prime minister Pierre Trudeau, directors Brian De Palma, writer/director Tom Mankiewicz and Steven Spielberg, as well as stand-up comedian Richard Pryor.
Oil dips on signs of ample supply despite OPEC cuts, Iran sanctions
With more than 1 200 people wounded by live fire, it was the deadliest day in Gaza since Hamas's last war with Israel in 2014. WTI light sweet oil was up 57 cents at USD71.52 a barrel, having touched the highest in 4 years.