Investments and Cash - Distribution of Fixed-Maturity Securities by Contractual Maturity (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Amortized Cost
Amortized cost	$ 9,310		$ 9,972
Estimated Fair Value
Estimated fair value	10,182		11,258
Fixed Maturities [Member]
Amortized Cost
Due within one year	156
Due after one year through five years	1,706
Due after five years through 10 years	2,146
Due after 10 years	3,584
Amortized cost	9,310
Estimated Fair Value
Due within one year	158
Due after one year through five years	1,763
Due after five years through 10 years	2,288
Due after 10 years	3,839
Estimated fair value	9,833		10,491
Fixed Maturities [Member] | RMBS [Member]
Amortized Cost
Amortized cost	1,145
Estimated Fair Value
Estimated fair value	1,185	[1]	1,285	[1]
Fixed Maturities [Member] | CMBS [Member]
Amortized Cost
Amortized cost	573
Estimated Fair Value
Estimated fair value	$ 600	[1]	$ 659	[1]

[1] Government-agency obligations were approximately 47% of mortgage backed securities as of March 31, 2015 and 44% as of December 31, 2014 based on fair value.