Investments - Problem Mortgage Loans (Details) (Commercial Real Estate Other Receivable [Member], USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Restructured problem mortgage loan, pre-modification	$ 31	$ 119
Restructured problem mortgage loan, number of contracts	2	1
Restructured problem loan, post-modification	31
Restructured problem mortgage loan, number of contracts - post-modification		2
Restructured problem loan, nature and extent of transaction	During 2013, the Company restructured its subordinate interest in two cross-collateralized pools of industrial loans totaling $31 million by extending the maturity dates and reducing the interest rates. This modification was considered a troubled debt restructuring and the loans were classified as problem mortgage loans because the borrower was experiencing financial difficulties and an interest rate concession was granted. No valuation reserves were required because the fair values of the underlying properties exceeded the carrying values of the outstanding loans.	During 2012, the Company restructured a $119 million problem mortgage loan, net of a valuation reserve, into two notes carried at $100 million and $19 million. The $100 million note was reclassified to impaired commercial mortgage loans with no valuation reserves and the $19 million note was classified as an other long-term investment. This modification was considered a troubled debt restructuring because the borrower was experiencing financial difficulties and an interest rate concession was granted. No valuation reserve was required because the fair value of the underlying property equaled the carrying value of the outstanding loan. Following the restructuring, the $100 million note was reclassified to good standing based on the results of the 2012 annual loan review and has been subsequently paid in full.
Problem And Potential Problem Mortgage Loans	160	215
Modified Loan 1 [Member]
Financing Receivable, Modifications [Line Items]
Restructured problem loan, post-modification		100
Modified Loan 2 [Member]
Financing Receivable, Modifications [Line Items]
Restructured problem loan, post-modification		$ 19