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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	$ 18	$ 19	$ 75	$ 71
Realized — impairments	(16)	(35)	(107)	(69)
Realized gains (losses) on securities	2	(16)	(32)	2
Net of tax noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	11	11	47	45
Realized — impairments	(10)	(21)	(66)	(43)
Realized gains (losses) on securities	1	(10)	(19)	2
Change in unrealized	87	(98)	440	(254)
Total pretax
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	18	19	75	71
Realized — impairments	(16)	(35)	(107)	(69)
Realized gains (losses) on securities	2	(16)	(32)	2
Change in unrealized	136	(155)	688	(398)
Fixed maturities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	5	7	36	17
Realized — impairments	(2)	(17)	(37)	(32)
Realized gains (losses) on securities	3	(10)	(1)	(15)
Change in unrealized	52	(9)	1,089	(414)
Equity securities
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	14	13	46	59
Realized — impairments	(16)	(23)	(83)	(48)
Realized gains (losses) on securities	(2)	(10)	(37)	11
Change in unrealized	89	(135)	77	(150)
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	(2)
Realized — impairments	0	0	0	0
Realized gains (losses) on securities	0	0	0	(2)
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	(1)	(1)	(7)	(3)
Realized — impairments	2	5	13	11
Realized gains (losses) on securities	1	4	6	8
Change in unrealized	(5)	(11)	(478)	166
Tax effects
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	(7)	(7)	(27)	(25)
Realized — impairments	5	13	38	25
Realized gains (losses) on securities	(2)	6	11	0
Change in unrealized	(48)	55	(241)	140
Noncontrolling interests
Realized gains (losses) and changes in unrealized appreciation (depreciation) related to fixed maturity and equity security investments
Realized before impairments	0	(1)	(1)	(1)
Realized — impairments	1	1	3	1
Realized gains (losses) on securities	1	0	2	0
Change in unrealized	$ (1)	$ 2	$ (7)	$ 4