Investments - Real Estate and Other Long-Term Investments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Other Long Term Investments [Line Items]
Other long-term investments	$ 1,488	$ 1,370
Carrying Value Of Non Income Producing Real Estate Entities And Securities Partnerships	264	217
Commitments to contribute to limited liability entities that hold real estate or loans to real estate	207
Commitments to contribute to entities that hold securities diversified by issuer and maturity date	476
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	916	909
Security Partnerships [Member]
Other Long Term Investments [Line Items]
Other long-term investments	456	357
Other Long Term Investments [Member]
Other Long Term Investments [Line Items]
Other long-term investments	$ 116	$ 104