Investments - Impaired Commercial Mortgage Loans (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 125	$ 125
Commercial Mortgage Loans Financing Receivable With Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	65	65
Commercial Mortgage Loans Financing Receivable With No Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	60	60
Impaired Commercial Mortgage Loans Gross [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	132	132
Impaired Commercial Mortgage Loans Gross [Member] | Commercial Mortgage Loans Financing Receivable With Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	72	72
Impaired Commercial Mortgage Loans Gross [Member] | Commercial Mortgage Loans Financing Receivable With No Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	60	60
Impaired Commercial Mortgage Loans Reserves [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	(7)	(7)
Impaired Commercial Mortgage Loans Reserves [Member] | Commercial Mortgage Loans Financing Receivable With Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	(7)	(7)
Impaired Commercial Mortgage Loans Reserves [Member] | Commercial Mortgage Loans Financing Receivable With No Related Allowance [Member]
Impaired Commercial Mortgage Loans And Valuation Reserves [Line Items]
Impaired Financing Receivable, Recorded Investment	$ 0	$ 0