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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		$ 36	$ 26	$ (25)	$ 52
Realized — impairments		(2)	(38)	(3)	(53)
Realized gains (losses) on securities		34	(12)	(28)	(1)
Net of tax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		28	17	(20)	34
Realized — impairments		(1)	(25)	(2)	(35)
Realized gains (losses) on securities		27	(8)	(22)	(1)
Change in unrealized		(98)	67	(526)	302
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		36	26	(25)	52
Realized — impairments		(2)	(38)	(3)	(53)
Realized gains (losses) on securities		34	(12)	(28)	(1)
Change in unrealized		(124)	104	(666)	465
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		0	9	3	25
Realized — impairments		(2)	(15)	(3)	(16)
Realized gains (losses) on securities		(2)	(6)	0	9
Change in unrealized		(213)	133	(1,150)	597
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		33	19	(39)	29
Realized — impairments		0	(29)	0	(49)
Realized gains (losses) on securities		33	(10)	(39)	(20)
Change in unrealized		0	24	0	116
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	3
Realized — impairments		0	0	0	0
Realized gains (losses) on securities		0	0	0	3
Change in unrealized		0	0	0	0
Other, Including DPAC and reserves related to the annuity business
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	[1]	3	(2)	11	(5)
Realized — impairments	[1]	0	6	0	12
Realized gains (losses) on securities	[1]	3	4	11	7
Change in unrealized	[1]	89	(53)	484	(248)
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments		(8)	(9)	5	(18)
Realized — impairments		1	13	1	18
Realized gains (losses) on securities		(7)	4	6	0
Change in unrealized		$ 26	$ (37)	$ 140	$ (163)

[1] Primarily adjustments to deferred policy acquisition costs and reserves related to the annuity business.