Investments (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available for Sale Securities
Amortized cost	$ 55,627	$ 57,201
Gross unrealized gains	2,244	1,707
Gross unrealized losses	(580)	(960)
Fixed income securities:	57,291	57,948
U.S. government and agencies
Schedule of Available for Sale Securities
Amortized cost	3,390	3,836
Gross unrealized gains	114	90
Gross unrealized losses	0	(4)
Fixed income securities:	3,504	3,922
Municipal
Schedule of Available for Sale Securities
Amortized cost	7,174	7,032
Gross unrealized gains	457	389
Gross unrealized losses	(15)	(20)
Fixed income securities:	7,616	7,401
Corporate
Schedule of Available for Sale Securities
Amortized cost	40,283	41,674
Gross unrealized gains	1,496	1,032
Gross unrealized losses	(507)	(879)
Fixed income securities:	41,272	41,827
Foreign government
Schedule of Available for Sale Securities
Amortized cost	999	983
Gross unrealized gains	55	50
Gross unrealized losses	0	0
Fixed income securities:	1,054	1,033
Asset-backed securities (“ABS”)
Schedule of Available for Sale Securities
Amortized cost	2,526	2,359
Gross unrealized gains	12	11
Gross unrealized losses	(39)	(43)
Fixed income securities:	2,499	2,327
Residential mortgage-backed securities (“RMBS”)
Schedule of Available for Sale Securities
Amortized cost	807	857
Gross unrealized gains	80	100
Gross unrealized losses	(12)	(10)
Fixed income securities:	875	947
Commercial mortgage-backed securities (“CMBS”)
Schedule of Available for Sale Securities
Amortized cost	427	438
Gross unrealized gains	27	32
Gross unrealized losses	(7)	(4)
Fixed income securities:	447	466
Redeemable preferred stock
Schedule of Available for Sale Securities
Amortized cost	21	22
Gross unrealized gains	3	3
Gross unrealized losses	0	0
Fixed income securities:	$ 24	$ 25