Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Financial Assets
Derivative Instruments, Gross amount of recognized assets	$ 2,250	$ 2,537
Derivative Instruments, Gross amounts offset	(713)	(677)
Derivative Instruments, Net amount of assets	1,537	1,860
Derivative Instruments, Cash collateral	(1,387)	(1,534)
Derivative Instruments, Net amount	$ 150	326
Embedded Derivative Instruments, Gross amount of recognized assets
Embedded Derivative Instruments, Gross amounts offset
Embedded Derivative Instruments, Net amount of assets
Embedded Derivative Instruments, Cash collateral
Embedded Derivative Instruments, Net amount
Total, Gross amount of recognized assets	$ 2,250	2,537
Total, Gross amounts offset	(713)	(677)
Total, Net amount of assets	1,537	1,860
Total, Cash collateral	(1,387)	(1,534)
Total, Net amount	150	326
Financial Liabilities
Derivative Instruments, Gross amount of recognized liabilities	139	130
Derivative Instruments, Gross amounts offset	(61)	(50)
Derivative Instruments, Net amount of liabilities	78	80
Derivative Instruments, Cash collateral	(143)	(85)
Derivative Instruments, Net amount	(65)	(5)
Embedded Derivative Instruments, Gross amount of recognized liabilities	$ 2,140	1,494
Embedded Derivative Instruments, Gross amounts offset
Embedded Derivative Instruments, Net amount of liabilities	$ 2,140	1,494
Embedded Derivative Instruments, Cash collateral
Embedded Derivative Instruments, Net amount	$ 2,140	1,494
Total, Gross amount of recognized liabilities	2,279	1,624
Total, Gross amounts offset	(61)	(50)
Total, Net amount of liabilities	2,218	1,574
Total, Cash collateral	(143)	(85)
Total, Net amount	$ 2,075	$ 1,489