Supplementary Insurance Information - Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 1,239	$ 1,184	$ 821
Reserves for future policy benefits, claims and unpaid losses and LAE	39,161	35,454	33,811
Unearned premiums	2,171	2,060	1,956
Net earned premiums	4,352	4,328	3,986
Net investment income	1,696	1,633	1,501
Benefits, claims, losses and settlement expenses	3,595	3,558	3,306
Amortization of deferred policy acquisition costs	673	653	646
Other operating expenses	1,443	1,369	1,155
Net written premiums (excluding life)	4,389	4,400	4,094
Property and casualty insurance
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	238	226	221
Reserves for future policy benefits, claims and unpaid losses and LAE	8,563	8,127	7,872
Unearned premiums	2,171	2,060	1,956
Net earned premiums	4,328	4,224	3,878
Net investment income	350	319	294
Benefits, claims, losses and settlement expenses	2,762	2,695	2,494
Amortization of deferred policy acquisition costs	520	511	485
Other operating expenses	870	839	746
Net written premiums (excluding life)	4,386	4,327	4,020
Annuity
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	981	934	564
Reserves for future policy benefits, claims and unpaid losses and LAE	29,907	26,622	23,764
Net investment income	1,356	1,224	1,136
Benefits, claims, losses and settlement expenses	800	732	648
Amortization of deferred policy acquisition costs	149	136	155
Other operating expenses	142	123	102
Run-off long-term care and life
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	20	24	36
Reserves for future policy benefits, claims and unpaid losses and LAE	691	705	2,175
Net earned premiums	24	104	108
Net investment income	21	80	82
Benefits, claims, losses and settlement expenses	33	131	164
Amortization of deferred policy acquisition costs	4	6	6
Other operating expenses	10	37	35
Net written premiums (excluding life)	3	73	74
Other
Supplementary Insurance Information, by Segment [Line Items]
Net investment income	(31)	10	(11)
Other operating expenses	$ 421	$ 370	$ 272