Investments and Cash - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions		Sep. 30, 2015		Dec. 31, 2014
Investments
Percent of Total	[1]	100.00%		100.00%
Amortized Cost		$ 10,768		$ 10,739
Gross Unrealized Gains		450		552
Gross Unrealized Losses		(56)		(33)
Estimated Fair Value		11,162		11,258
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 2	[2]	$ 8
Fixed Maturities [Member]
Investments
Percent of Total	[1]	95.00%		93.00%
Amortized Cost		$ 10,242		$ 9,972
Gross Unrealized Gains		450		552
Gross Unrealized Losses		(52)		(33)
Estimated Fair Value		10,640		10,491
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 2	[2]	$ 8
Short-term Investments [Member]
Investments
Percent of Total	[1]	5.00%		7.00%
Amortized Cost		$ 526		$ 767
Gross Unrealized Gains		0		0
Gross Unrealized Losses		(4)		0
Estimated Fair Value		522		767
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 0	[2]	$ 0
Obligations of state and political subdivisions [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	53.00%		50.00%
Amortized Cost		$ 5,668		$ 5,416
Gross Unrealized Gains		308		380
Gross Unrealized Losses		(18)		(1)
Estimated Fair Value		5,958		5,795
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 3	[2]	$ 7
US Treasury and Government [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	4.00%		6.00%
Amortized Cost		$ 449		$ 635
Gross Unrealized Gains		28		31
Gross Unrealized Losses		0		(1)
Estimated Fair Value		477		665
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 0	[2]	$ 0
Corporate securities [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	13.00%		12.00%
Amortized Cost		$ 1,403		$ 1,320
Gross Unrealized Gains		45		53
Gross Unrealized Losses		(12)		(5)
Estimated Fair Value		1,436		1,368
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ (3)	[2]	$ (2)
RMBS [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1],[3]	13.00%		12.00%
Amortized Cost	[3]	$ 1,349		$ 1,255
Gross Unrealized Gains	[3]	38		51
Gross Unrealized Losses	[3]	(16)		(21)
Estimated Fair Value	[3]	1,371		1,285
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment	[3]	$ (2)	[2]	$ 0
CMBS [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1],[3]	4.00%		6.00%
Amortized Cost	[3]	$ 492		$ 639
Gross Unrealized Gains	[3]	19		20
Gross Unrealized Losses	[3]	0		0
Estimated Fair Value	[3]	511		659
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment	[3]	$ 0	[2]	$ 0
Asset-backed Securities [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	5.00%		4.00%
Amortized Cost		$ 584		$ 411
Gross Unrealized Gains		6		9
Gross Unrealized Losses		0		(3)
Estimated Fair Value		590		417
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 4	[2]	$ 3
Foreign government securities [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	3.00%		3.00%
Amortized Cost		$ 297		$ 296
Gross Unrealized Gains		6		8
Gross Unrealized Losses		(6)		(2)
Estimated Fair Value		297		302
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 0	[2]	$ 0

[1] Based on amortized cost.

[2] Accumulated OCI. See also Note 18, Shareholders' Equity.

[3] Government-agency obligations were approximately 55% of mortgage backed securities as of September 30, 2015 and 44% as of December 31, 2014 based on fair value.