Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Asset Derivatives	$ 336	$ 470
Derivative Asset		135
Gross Amounts of Recognized (Liabilities)	(776)	(908)
Derivative Financial Instruments, Assets [Member] | Other Investments and Other Liabilities
Derivative [Line Items]
Asset Derivatives	307	380
Gross Amounts Offset in the Statement of Financial Position, assets	270	338
Derivative Asset	40	135
Accrued Interest and Cash Collateral Pledged	3	93
Financial Collateral Pledged	3	0
Net Amount, assets	34	42
Derivative Financial Instruments, Liabilities [Member] | Other Investments and Other Liabilities
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(758)	(833)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(119)	(154)
Derivative liabilities	(491)	(588)
Accrued Interest and Cash Collateral (Received)	(148)	(91)
Financial Collateral (Received)	(638)	(674)
Net amount, liabilities	$ (1)	$ (5)