Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Asset Derivatives	$ 355	$ 470
Derivative Asset		135
Gross Amounts of Recognized (Liabilities)	(816)	(908)
Other Investments and Other Liabilities | Derivative Financial Instruments, Liabilities [Member]
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(800)	(833)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(112)	(154)
Derivative liabilities	(575)	(588)
Accrued Interest and Cash Collateral (Received)	(113)	(91)
Financial Collateral (Received)	(688)	(674)
Net amount, liabilities	0	(5)
Other Investments and Other Liabilities | Derivative Financial Instruments, Assets [Member]
Derivative [Line Items]
Asset Derivatives	301	380
Gross Amounts Offset in the Statement of Financial Position, assets	268	338
Derivative Asset	76	135
Accrued Interest and Cash Collateral Pledged	43	93
Financial Collateral Pledged	2	0
Net Amount, assets	$ 31	$ 42