Supplementary Insurance Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 1,184	$ 821	$ 975
Reserves for future policy benefits, claims and unpaid losses and LAE	35,454	33,811	29,362
Unearned premiums	2,060	1,956	1,757
Net earned premiums	4,328	3,986	3,318
Net investment income	1,633	1,501	1,346
Benefits, claims, losses and settlement expenses	3,558	3,306	2,731
Amortization of deferred policy acquisition costs	653	646	610
Other operating expenses	1,369	1,155	1,073
Net written premiums (excluding life)	4,400	4,094	3,417
Property and Casualty Insurance [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	226	221	211
Reserves for future policy benefits, claims and unpaid losses and LAE	8,127	7,872	6,410
Unearned premiums	2,060	1,956	1,757
Net earned premiums	4,224	3,878	3,204
Net investment income	319	294	263
Benefits, claims, losses and settlement expenses	2,695	2,494	2,040
Amortization of deferred policy acquisition costs	511	485	460
Other operating expenses	839	746	607
Net written premiums (excluding life)	4,327	4,020	3,341
Annuity [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	934	564	723
Reserves for future policy benefits, claims and unpaid losses and LAE	26,622	23,764	20,944
Net investment income	1,224	1,136	1,034
Benefits, claims, losses and settlement expenses	732	648	531
Amortization of deferred policy acquisition costs	136	155	144
Other operating expenses	123	102	113
Run-off Long-term Care and Life [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	24	36	41
Reserves for future policy benefits, claims and unpaid losses and LAE	705	2,175	2,008
Net earned premiums	104	108	114
Net investment income	80	82	76
Benefits, claims, losses and settlement expenses	131	164	160
Amortization of deferred policy acquisition costs	6	6	6
Other operating expenses	37	35	39
Net written premiums (excluding life)	73	74	76
Other [Member]
Supplementary Insurance Information, by Segment [Line Items]
Net investment income	10	(11)	(27)
Other operating expenses	$ 370	$ 272	$ 314