Investments and Cash - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income
Gross investment income									$ 387	$ 404	$ 426
Investment expenses									(9)	(9)	(9)
Net investment income	$ 82	$ 88	$ 110	$ 98	$ 98	$ 99	$ 98	$ 100	378	395	417
Income from fixed-maturity securities managed by third parties [Member]
Net Investment Income
Gross investment income									273	297	298
Income from internally managed securities [Member]
Net Investment Income
Gross investment income									$ 114	$ 107	$ 128