Supplementary Insurance Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 821	$ 975	$ 550
Reserves for future policy benefits, claims and unpaid losses and LAE	33,811	29,362	26,513
Unearned premiums	1,956	1,757	1,651
Net earned premiums	3,986	3,318	3,165
Net investment income	1,501	1,346	1,301
Benefits, claims, losses and settlement expenses	3,306	2,731	2,770
Amortization of deferred policy acquisition costs	646	610	700
Other operating expenses	1,135	1,062	950
Net written premiums (excluding life)	4,094	3,417	3,227
Property and Casualty Insurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	221	211	204
Reserves for future policy benefits, claims and unpaid losses and LAE	7,872	6,410	6,845
Unearned premiums	1,956	1,757	1,651
Net earned premiums	3,878	3,204	2,847
Net investment income	294	263	275
Benefits, claims, losses and settlement expenses	2,494	2,040	1,873
Amortization of deferred policy acquisition costs	485	460	423
Other operating expenses	746	607	528
Net written premiums (excluding life)	4,020	3,341	2,949
Annuity [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	564	723	299
Reserves for future policy benefits, claims and unpaid losses and LAE	23,764	20,944	17,609
Net investment income	1,136	1,034	976
Benefits, claims, losses and settlement expenses	648	531	541
Amortization of deferred policy acquisition costs	155	144	163
Other operating expenses	83	103	68
Run-off Long-term Care and Life [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	36	41	47
Reserves for future policy benefits, claims and unpaid losses and LAE	2,175	2,008	2,059
Net earned premiums	108	114	119
Net investment income	82	76	69
Benefits, claims, losses and settlement expenses	164	160	225
Amortization of deferred policy acquisition costs	6	6	95
Other operating expenses	34	38	28
Net written premiums (excluding life)	74	76	79
Medicare Supplement and Critical Illness [Member]
Supplementary Insurance Information, by Segment [Line Items]
Net earned premiums			199
Net investment income			7
Benefits, claims, losses and settlement expenses			131
Amortization of deferred policy acquisition costs			19
Other operating expenses			34
Net written premiums (excluding life)			199
Other [Member]
Supplementary Insurance Information, by Segment [Line Items]
Net investment income	(11)	(27)	(26)
Other operating expenses	$ 272	$ 314	$ 292