Investments (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	$ 23,770	$ 25,822
Gross unrealized gain	1,321	2,486
Gross unrealized loss	(462)	(191)
Fair Value	24,629	28,117
U.S. government and agencies
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	920	668
Gross unrealized gain	57	102
Gross unrealized loss	0	0
Fair Value	977	770
Municipal
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	2,162	3,156
Gross unrealized gain	292	520
Gross unrealized loss	(12)	(14)
Fair Value	2,442	3,662
Corporate
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	18,069	19,465
Gross unrealized gain	849	1,670
Gross unrealized loss	(414)	(150)
Fair Value	18,504	20,985
Foreign government
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	348	654
Gross unrealized gain	36	81
Gross unrealized loss	0	0
Fair Value	384	735
ABS
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	1,443	773
Gross unrealized gain	5	13
Gross unrealized loss	(28)	(21)
Fair Value	1,420	765
RMBS
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	406	554
Gross unrealized gain	49	55
Gross unrealized loss	(4)	(4)
Fair Value	451	605
CMBS
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	409	538
Gross unrealized gain	31	43
Gross unrealized loss	(4)	(2)
Fair Value	436	579
Redeemable preferred stock
Amortized cost, gross unrealized gains and losses and fair value for fixed income securities
Amortized cost	13	14
Gross unrealized gain	2	2
Gross unrealized loss	0	0
Fair Value	$ 15	$ 16