Investments - Problem Mortgage Loans (Details) (Commercial Real Estate Other Receivable [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Jun. 30, 2013
Financing Receivable, Modifications [Line Items]
Restructured problem mortgage loan, pre-modification	$ 119
Restructured problem mortgage loan, number of contracts	1
Restructured problem loan, nature and extent of transaction	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. Other loans were modified during the six months ended June 30, 2013 and the twelve months ended December 31, 2012, but were not considered troubled debt restructures. The impact of modifications to these loans was not material to the Company’s results of operations, financial condition or liquidity.
Problem And Potential Problem Mortgage Loans	215	160
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