Investments (Repurchase Agreements - Securities Lending Remaining Tenor) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Securities Financing Transaction [Line Items]
Total	$ 32,119	$ 30,197
Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	101	50
Other Debt Obligations [Member] | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	74	25
Foreign corporate
Securities Financing Transaction [Line Items]
Total	31	0
Foreign corporate | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	27	25
Maturity Less than 30 Days
Securities Financing Transaction [Line Items]
Total	11,420	12,998
Maturity Less than 30 Days | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	51	0
Maturity Less than 30 Days | Other Debt Obligations [Member] | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	37	0
Maturity Less than 30 Days | Foreign corporate
Securities Financing Transaction [Line Items]
Total	31	0
Maturity Less than 30 Days | Foreign corporate | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	14	0
Maturity 30 to 90 Days | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	50	50
Maturity 30 to 90 Days | Other Debt Obligations [Member] | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	37	25
Maturity 30 to 90 Days | Foreign corporate | Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Total	$ 13	$ 25