Investments - Valuation Reserves for Commercial Mortgage Loans (Details) (Mortgage Loans on Real Estate [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Mortgage Loans on Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Reserve balance, January 1,	$ 8	$ 7
Increase in valuation reserves	4	4
Charge-offs upon sales and repayments, net of recoveries	0	(3)
Reserve balance, December 31,	$ 12	$ 8