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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	$ 26	$ 18	$ 52	$ 75
Realized — impairments	(38)	(16)	(53)	(107)
Realized gains (losses) on securities	(12)	2	(1)	(32)
Net of tax and noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	17	11	34	47
Realized — impairments	(25)	(10)	(35)	(66)
Realized gains (losses) on securities	(8)	1	(1)	(19)
Change in unrealized	67	87	302	440
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	26	18	52	75
Realized — impairments	(38)	(16)	(53)	(107)
Realized gains (losses) on securities	(12)	2	(1)	(32)
Change in unrealized	104	136	465	688
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	9	5	25	36
Realized — impairments	(15)	(2)	(16)	(37)
Realized gains (losses) on securities	(6)	3	9	(1)
Change in unrealized	133	52	597	1,089
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	19	14	29	46
Realized — impairments	(29)	(16)	(49)	(83)
Realized gains (losses) on securities	(10)	(2)	(20)	(37)
Change in unrealized	24	89	116	77
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	3	0
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	0	0	3	0
Change in unrealized	0	0	0	0
Other, Including DPAC and reserves on annuities and long-term care
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(2)	(1)	(5)	(7)
Realized — impairments	6	2	12	13
Realized gains (losses) on securities	4	1	7	6
Change in unrealized	(53)	(5)	(248)	(478)
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(9)	(7)	(18)	(27)
Realized — impairments	13	5	18	38
Realized gains (losses) on securities	4	(2)	0	11
Change in unrealized	(37)	(48)	(163)	(241)
Noncontrolling interests
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	1	0	3
Realized gains (losses) on securities	0	1	0	2
Change in unrealized	$ 0	$ (1)	$ 0	$ (7)