Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Asset Derivatives	$ 628	$ 623
Derivative Asset		135
Gross Amounts of Recognized (Liabilities)	(953)	(1,061)
Derivative Financial Instruments, Assets [Member] | Other Investments and Other Liabilities
Derivative [Line Items]
Asset Derivatives	516	533
Gross Amounts Offset in the Statement of Financial Position, assets	478	491
Derivative Asset	78	135
Accrued Interest and Cash Collateral Pledged	40	93
Financial Collateral Pledged	1	0
Net Amount, assets	37	42
Derivative Financial Instruments, Liabilities [Member] | Other Investments and Other Liabilities
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(900)	(986)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(301)	(307)
Derivative liabilities	(462)	(588)
Accrued Interest and Cash Collateral (Received)	(137)	(91)
Financial Collateral (Received)	(596)	(674)
Net amount, liabilities	$ (3)	$ (5)