Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014
Amortized Cost
Amortized cost		$ 10,229	$ 9,972
Estimated Fair Value
Estimated fair value		11,416	11,258
Fixed Maturities [Member]
Amortized Cost
Due within one year		217
Due after one year through five years		1,660
Due after five years through 10 years		2,200
Due after 10 years		4,251
Amortized cost		10,229
Estimated Fair Value
Due within one year		220
Due after one year through five years		1,717
Due after five years through 10 years		2,299
Due after 10 years		4,416
Estimated fair value		10,582	10,491
Fixed Maturities [Member] | RMBS [Member]
Amortized Cost
Amortized cost		1,313
Estimated Fair Value
Estimated fair value	[1]	1,329	1,285
Fixed Maturities [Member] | CMBS [Member]
Amortized Cost
Amortized cost		588
Estimated Fair Value
Estimated fair value	[1]	$ 601	$ 659

[1] 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.