Investments - Real Estate and Other Long-Term Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Other Long Term Investments [Line Items]
Other long-term investments	$ 1,404	$ 1,488
Carrying Value Of Non Income Producing Real Estate Entities And Securities Partnerships	277	264
Commitments to contribute to limited liability entities that hold real estate or loans to real estate	184
Commitments to contribute to entities that hold securities diversified by issuer and maturity date	$ 487
Percentage of the committed amounts to be disbursed by the end of next year	40.00%
Real Estate Entities [Member]
Other Long Term Investments [Line Items]
Other long-term investments	$ 814	916
Security Partnerships [Member]
Other Long Term Investments [Line Items]
Other long-term investments	501	456
Other Long Term Investments [Member]
Other Long Term Investments [Line Items]
Other long-term investments	$ 89	$ 116