Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Financial Assets
Derivative Instruments, Gross amount of recognized assets	$ 3,793	$ 2,250
Derivative Instruments, Gross amounts offset	(1,180)	(713)
Derivative Instruments, Net amount of assets	2,613	1,537
Derivative Instruments, Cash collateral	(3,004)	(1,387)
Derivative Instruments, Net amount	(391)	150
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	3,793	2,250
Total, Gross amounts offset	(1,180)	(713)
Total, Net amount of assets	2,613	1,537
Total, Cash collateral	(3,004)	(1,387)
Total, Net amount	(391)	150
Financial Liabilities
Derivative Instruments, Gross amount of recognized liabilities	268	139
Derivative Instruments, Gross amounts offset	(130)	(61)
Derivative Instruments, Net amount of liabilities	138	78
Derivative Instruments, Cash collateral	(391)	(143)
Derivative Instruments, Net amount	(253)	(65)
Embedded Derivative Instruments, Gross amount of recognized liabilities	3,694	2,140
Embedded Derivative Instruments, Gross amounts offset
Embedded Derivative Instruments, Net amount of liabilities	3,694	2,140
Embedded Derivative Instruments, Cash collateral
Embedded Derivative Instruments, Net amount	3,694	2,140
Total, Gross amount of recognized liabilities	3,962	2,279
Total, Gross amounts offset	(130)	(61)
Total, Net amount of liabilities	3,832	2,218
Total, Cash collateral	(391)	(143)
Total, Net amount	$ 3,441	$ 2,075