Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	$ 1,221		$ 1,221			$ 1,129
Accumulated other comprehensive income, net of tax, end of period	1,221		1,221			1,129
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated unrealized gains, net, on investments available for sale, before tax, beginning of period	2,231	1,717	1,875	1,489
Other comprehensive income before reclassification, before tax	(230)	(47)	164	194
Reclassification adjustment for realized gains, net, included in net income, before tax	(14)	(6)	(52)	(19)
Effect on other comprehensive income, before tax	(244)	(53)	112	175
Accumulated unrealized gains, net, on investments available for sale, before tax, end of period	1,987	1,664	1,987	1,664
Accumulated Other Comprehensive Income Loss Tax [Abstract]
Accumulated unrealized gains, net, on investments available for sale and other invested assets, tax, beginning of period	686	573	686	573
Other comprehensive income before reclassification, tax	(81)	(17)	56	67
Reclassification adjustment for realized gains, net, included in net income, tax	(4)	(2)	(17)	(6)
Effect on other comprehensive income, tax	(85)	(19)	39	61
Accumulated unrealized gains, net, on investments available for sale and other invested assets, tax, end of period	771	592	647	512
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated unrealized gains, net, on investments available for sale and other invested assets, net of tax, beginning of period	1,460	1,125	1,228	977
Other comprehensive income before reclassification , net of tax	(149)	(30)	108	127
Reclassification adjustment for realized gains, net, included in net income, net of tax	(10)	(4)	(35)	(13)
Effect on other comprehensive income, net of tax	(159)	(34)	73	114
Accumulated unrealized gains, net, on investments available for sale and other invested assets, net of tax, end of period	1,301	1,091	1,301	1,091
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Other comprehensive income before reclassification, before tax	0	0	0	0
Accumulated unrealized losses, net, for pension obligations, before Tax, beginning of period	(99)	(86)	(101)	(88)
Reclassification adjustment for amortization of actuarial loss and prior service cost, net, included in net income, before tax	3	1	5	3
Effect on other comprehensive income, before tax	3	1	5	3
Accumulated unrealized losses, net, for pension obligations, before Tax, end of period	(96)	(85)	(96)	(85)
Accumulated Other Comprehensive Income Loss Tax [Abstract]
Other comprehensive income before reclassification, tax	0	0	0	0
Accumulated unrealized losses, net, for pension obligations, tax, beginning of period	(34)	(30)	(35)	(31)
Reclassification adjustment for amortization of actuarial loss and prior service cost, net, included in net income, tax	1	0	2	1
Effect on other comprehensive income, tax	1	0	2	1
Accumulated unrealized losses, net, for pension obligations, tax, end of period	(33)	(30)	(33)	(30)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Other comprehensive income before reclassification , net of tax	0	0	0	0
Accumulated unrealized losses, net, for pension obligations, net of tax, beginning of period	(65)	(56)	(66)	(57)
Reclassification adjustment for amortization of actuarial loss and prior service cost,net, included in net income, net of tax	2	1	3	2
Effect on other comprehensive income, net of tax	2	1	3	2
Accumulated unrealized losses, net, for pension obligations, net of tax, end of period	(63)	(55)	(63)	(55)
Accumulated Net Unrealized Gain (Loss) on Deferred Costs, Reserves And Other
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, before tax, beginning of period	(50)	(34)	(50)	(29)
Effect on other comprehensive income, before tax	24	(5)	24	(10)
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, before tax, end of period	(26)	(39)	(26)	(39)
Accumulated Other Comprehensive Income Loss Tax [Abstract]
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, tax, beginning of period	(17)	(12)	(17)	(10)
Effect on other comprehensive income, tax	8	(1)	8	(3)
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, tax, end of period	(9)	(13)	(9)	(13)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, beginning of period, net of tax	(33)	(22)	(33)	(19)
Effect on other comprehensive income, net of tax	16	(4)	16	(7)
Accumulated unrealized losses, net, on life deferred acquisition costs, life policy reserves and other, end of period, net of tax	(17)	(26)	(17)	(26)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income Loss Before Tax [Abstract]
Accumulated other comprehensive income, before taxes, beginning of period	2,082	1,597	1,724	1,372
Change in unrealized gains, net, on investments available for sale, before Tax	(244)	(53)	112	175
Change in pension obligations, before tax	3	1	5	3
Change in life deferred acquisition costs, life policy reserves and other, before Tax	24	(5)	24	(10)
Effect on other comprehensive income, before Tax	(217)	(57)	141	168
Accumulated other comprehensive income, before taxes, end of period	1,865	1,540	1,865	1,540
Accumulated Other Comprehensive Income Loss Tax [Abstract]
Accumulated other comprehensive income, tax, beginning of period	720	550	595	471
Change in unrealized gains, net, on investments available for sale and other invested assets, tax	(85)	(19)	39	61
Change in pension obligations, tax	1	0	2	1
Change in life deferred acquisition costs, life policy reserves and other, tax	8	(1)	8	(3)
Effect on other comprehensive income, tax	(76)	(20)	49	59
Accumulated other comprehensive income, tax, end of period	644	530	644	530
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated other comprehensive income, net of tax, beginning of period	1,221	1,010	1,221	1,010	1,362	1,129	1,047	901
Change in unrealized gains, net, on investments available for sale, net of tax	(159)	(34)	73	114
Change in pension obligations, net of tax	2	1	3	2
Change in life deferred acquisition costs, life policy reserves and other, net of tax	16	(4)	16	(7)
Effect on other comprehensive income, net of tax	(141)	(37)	92	109
Accumulated other comprehensive income, net of tax, end of period	$ 1,221	$ 1,010	$ 1,221	$ 1,010	$ 1,362	$ 1,129	$ 1,047	$ 901