Investments - Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized gains (losses) on securities	$ 43	$ 108	$ 120	$ (220)
Net of tax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	34	85	94	(163)
Realized — impairments	0	0	1	(11)
Realized gains (losses) on securities	34	85	95	(174)
Change in unrealized	16	203	(19)	(16)
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	43	108	119	(206)
Realized — impairments	0	0	1	(14)
Realized gains (losses) on securities	43	108	120	(220)
Change in unrealized	20	257	(24)	(20)
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	1	1	0	4
Realized — impairments	0	0	1	(14)
Realized gains (losses) on securities	1	1	1	(10)
Change in unrealized	20	257	(24)	(20)
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	42	107	119	(211)
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	42	107	119	(211)
Change in unrealized	0	0	0	0
Mortgage loans and other investments
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	0	0	0	1
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	0	0	0	1
Change in unrealized	0	0	0	0
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(9)	(23)	(25)	43
Realized — impairments	0	0	0	3
Realized gains (losses) on securities	(9)	(23)	(25)	46
Change in unrealized	$ (4)	$ (54)	$ 5	$ 4