Quarterly Financial Data (Unaudited) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of quarterly financial data
Revenues	$ 139	$ 76	$ 349	$ 266	$ 377	$ 388	$ 418	$ 432	$ 830	$ 1,615	$ 1,461
Pretax income	120	46	114	42	132	131	130	119	322	512	416
Net income	$ 71	$ 26	$ 82	$ 22	$ 93	$ 110	$ 112	$ 103	$ 201	$ 418	$ 387