Investments (Securities Lending Remaining Tenor) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 30,511	$ 30,826
Percentage of Remaining Contractual Tenor of Securities on Loan	100.00%	100.00%
U.S. Treasury and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 27,069	$ 26,033
Percentage of Remaining Contractual Tenor of Securities on Loan	88.70%	84.50%
RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 1,930	$ 3,054
Percentage of Remaining Contractual Tenor of Securities on Loan	6.40%	9.90%
Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 1,197	$ 1,145
Percentage of Remaining Contractual Tenor of Securities on Loan	3.90%	3.70%
U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 276	$ 307
Percentage of Remaining Contractual Tenor of Securities on Loan	0.90%	1.00%
Foreign corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 39	$ 287
Percentage of Remaining Contractual Tenor of Securities on Loan	0.10%	0.90%
Maturity Overnight [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 10,621	$ 10,701
Maturity Overnight [Member] | U.S. Treasury and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	10,610	10,371
Maturity Overnight [Member] | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity Overnight [Member] | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	5	30
Maturity Overnight [Member] | U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	125
Maturity Overnight [Member] | Foreign corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6	175
Maturity Less than 30 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	10,184	12,233
Maturity Less than 30 Days [Member] | U.S. Treasury and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	8,731	10,423
Maturity Less than 30 Days [Member] | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	170	482
Maturity Less than 30 Days [Member] | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	974	1,034
Maturity Less than 30 Days [Member] | U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	276	182
Maturity Less than 30 Days [Member] | Foreign corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	33	112
Maturity 30 to 90 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	8,825	7,892
Maturity 30 to 90 Days [Member] | U.S. Treasury and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,847	5,239
Maturity 30 to 90 Days [Member] | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,760	2,572
Maturity 30 to 90 Days [Member] | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	218	81
Maturity 30 to 90 Days [Member] | U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity 30 to 90 Days [Member] | Foreign corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity Greater than 90 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	881	0
Maturity Greater than 90 Days [Member] | U.S. Treasury and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	881	0
Maturity Greater than 90 Days [Member] | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity Greater than 90 Days [Member] | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity Greater than 90 Days [Member] | U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Maturity Greater than 90 Days [Member] | Foreign corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 0	$ 0