Income Taxes - Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current income tax expense:
State income tax	$ 2	$ 0	$ 3
Canadian federal and provincial income tax	48	51	109
Total current income tax expense	50	51	112
Deferred income tax expense/(benefit):
Canadian federal and provincial income tax	23	(70)	(46)
Total deferred income tax expense/(benefit)	23	(70)	(46)
Total income tax expense/(benefit)	$ 73	$ (19)	$ 66