Investments and Cash - Fixed Maturity Securities and Short Term Investments (Details) - USD ($) $ in Millions		Jun. 30, 2015		Dec. 31, 2014
Investments
Percent of Total	[1]	100.00%		100.00%
Amortized Cost		$ 11,063		$ 10,739
Gross Unrealized Gains		422		552
Gross Unrealized Losses		(69)		(33)
Estimated fair value		11,416		11,258
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 9	[2]	$ 8
Fixed Maturities [Member]
Investments
Percent of Total	[1]	93.00%		93.00%
Amortized Cost		$ 10,229		$ 9,972
Gross Unrealized Gains		422		552
Gross Unrealized Losses		(69)		(33)
Estimated fair value		10,582		10,491
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 9	[2]	$ 8
Short-term Investments [Member]
Investments
Percent of Total	[1]	7.00%		7.00%
Amortized Cost		$ 834		$ 767
Gross Unrealized Gains		0		0
Gross Unrealized Losses		0		0
Estimated fair value		834		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]	52.00%		50.00%
Amortized Cost		$ 5,736		$ 5,416
Gross Unrealized Gains		278		380
Gross Unrealized Losses		(28)		(1)
Estimated fair value		5,986		5,795
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 2	[2]	$ 7
US Treasury and Government [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	4.00%		6.00%
Amortized Cost		$ 459		$ 635
Gross Unrealized Gains		28		31
Gross Unrealized Losses		(1)		(1)
Estimated fair value		486		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		$ 1,415		$ 1,320
Gross Unrealized Gains		42		53
Gross Unrealized Losses		(15)		(5)
Estimated fair value		1,442		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]	12.00%		12.00%
Amortized Cost	[3]	$ 1,313		$ 1,255
Gross Unrealized Gains	[3]	38		51
Gross Unrealized Losses	[3]	(22)		(21)
Estimated fair value	[3]	1,329		1,285
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment	[3]	$ (1)	[2]	$ 0
CMBS [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1],[3]	5.00%		6.00%
Amortized Cost	[3]	$ 588		$ 639
Gross Unrealized Gains	[3]	14		20
Gross Unrealized Losses	[3]	(1)		0
Estimated fair value	[3]	601		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]	4.00%		4.00%
Amortized Cost		$ 416		$ 411
Gross Unrealized Gains		15		9
Gross Unrealized Losses		0		(3)
Estimated fair value		431		417
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 10	[2]	$ 3
Foreign government securities [Member] | Fixed Maturities [Member]
Investments
Percent of Total	[1]	3.00%		3.00%
Amortized Cost		$ 302		$ 296
Gross Unrealized Gains		7		8
Gross Unrealized Losses		(2)		(2)
Estimated fair value		307		302
AOCI Gain (Loss) on Securities with Other-Than-Temporary Impairment		$ 1	[2]	$ 0

[1] Based on amortized cost.

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

[3] Government-agency obligations were approximately 53% of mortgage backed securities as of June 30, 2015 and 44% as of December 31, 2014 based on fair value.