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
	Mar. 31, 2021	Mar. 31, 2020
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized gains (losses) on securities	$ 77	$ (328)
Net of tax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	60	(248)
Realized — impairments	1	(11)
Realized gains (losses) on securities	61	(259)
Change in unrealized	(35)	(219)
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	76	(314)
Realized — impairments	1	(14)
Realized gains (losses) on securities	77	(328)
Change in unrealized	(44)	(277)
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(1)	3
Realized — impairments	1	(14)
Realized gains (losses) on securities	0	(11)
Change in unrealized	(44)	(277)
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	77	(318)
Realized — impairments	0	0
Realized gains (losses) on securities	77	(318)
Change in unrealized	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	1
Realized — impairments	0	0
Realized gains (losses) on securities	0	1
Change in unrealized	0	0
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(16)	66
Realized — impairments	0	3
Realized gains (losses) on securities	(16)	69
Change in unrealized	$ 9	$ 58