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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized gains (losses) on securities	$ (17)	$ 23	$ 103	$ (197)
Net of tax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(12)	18	82	(145)
Realized — impairments	0	0	1	(11)
Realized gains (losses) on securities	(12)	18	83	(156)
Change in unrealized	(27)	47	(46)	31
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(17)	23	102	(183)
Realized — impairments	0	0	1	(14)
Realized gains (losses) on securities	(17)	23	103	(197)
Change in unrealized	(35)	59	(59)	39
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(2)	1	(2)	5
Realized — impairments	0	0	1	(14)
Realized gains (losses) on securities	(2)	1	(1)	(9)
Change in unrealized	(35)	59	(59)	39
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(15)	22	104	(189)
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	(15)	22	104	(189)
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	5	(5)	(20)	38
Realized — impairments	0	0	0	3
Realized gains (losses) on securities	5	(5)	(20)	41
Change in unrealized	$ 8	$ (12)	$ 13	$ (8)