Derivative Instruments (Balance Sheet Offsetting) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Financial Assets
Derivative Instruments, Gross amount of recognized assets	$ 1,600	$ 1,470
Derivative Instruments, Gross amounts offset	(546)	(543)
Derivative Instruments, Net amount of assets	1,054	927
Derivative Instruments, Cash collateral	(1,054)	(894)
Derivative Instruments, Net amount		33
Embedded Derivative Instruments, Gross amount of recognized assets	298
Embedded Derivative Instruments, Gross amounts offset
Embedded Derivative Instruments, Net amount of assets	298
Embedded Derivative Instruments, Cash collateral
Embedded Derivative Instruments, Net amount	298
Total, Gross amount of recognized assets	1,898	1,470
Total, Gross amounts offset	(546)	(543)
Total, Net amount of assets	1,352	927
Total, Cash collateral	(1,054)	(894)
Total, Net amount	298	33
Financial Liabilities
Derivative Instruments, Gross amount of recognized liabilities	611	1,089
Derivative Instruments, Gross amounts offset	(121)	(536)
Derivative Instruments, Net amount of liabilities	490	553
Derivative Instruments, Cash collateral	(527)	(630)
Derivative Instruments, Net amount	(37)	(77)
Embedded Derivative Instruments, Gross amount of recognized liabilities	1,321	1,563
Embedded Derivative Instruments, Gross amounts offset
Embedded Derivative Instruments, Net amount of liabilities	1,321	1,563
Embedded Derivative Instruments, Cash collateral
Embedded Derivative Instruments, Net amount	1,321	1,563
Total, Gross amount of recognized liabilities	1,932	2,652
Total, Gross amounts offset	(121)	(536)
Total, Net amount of liabilities	1,811	2,116
Total, Cash collateral	(527)	(630)
Total, Net amount	$ 1,284	$ 1,486