Investments, Net Investment Income (Details) $ in Millions		12 Months Ended
		Dec. 31, 2020 USD ($) Investment	Dec. 31, 2019 USD ($) Investment	Dec. 31, 2018 USD ($)
Net Investment Income [Abstract]
Investment income		$ 2,071	$ 2,430	$ 1,878
Investment expenses		(76)	(75)	(61)
Net investment income		1,995	2,355	1,817
Net unrealized gains (losses) on securities		$ 88	$ 41	(121)
Number of investments in single issuer exceeding 10% | Investment		0	0
Fixed Maturity Securities [Member]
Net Investment Income [Abstract]
Investment income		$ 1,728	$ 1,817	1,795
Limited Partnership Investments [Member]
Net Investment Income [Abstract]
Investment income		127	204	22
Short Term Investments [Member]
Net Investment Income [Abstract]
Investment income		10	52	43
Equity Securities [Member]
Net Investment Income [Abstract]
Investment income		65	85	18
Income (Loss) from Trading Portfolio [Member]
Net Investment Income [Abstract]
Investment income	[1]	83	216	(54)
Other [Member]
Net Investment Income [Abstract]
Investment income		$ 58	$ 56	$ 54

[1] Net unrealized gains (losses) related to changes in fair value on securities still held were $88, $41 and $(121) for the years ended December 31, 2020, 2019 and 2018.