Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Asset Derivatives	$ 469	$ 86
Derivative assets	10	(415)
Accrued Interest and Cash Collateral Pledged	1	489
Gross Amounts of Recognized (Liabilities)	(559)	(612)
Derivative liabilities	(100)	(112)
Derivative Assets | Other Investments and Other Liabilities
Derivative [Line Items]
Asset Derivatives	469	85
Gross Amounts Offset in the Statement of Financial Position, assets	466	82
Derivative assets	10	(415)
Accrued Interest and Cash Collateral Pledged		418
Financial Collateral Pledged	1	2
Net Amount, assets	2	1
Accrued Interest and Cash Collateral (Received)	(7)
Derivative Liabilities | Other Investments and Other Liabilities
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(559)	(612)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(454)	(488)
Derivative liabilities	(100)	(112)
Accrued Interest and Cash Collateral (Received)	(5)	(12)
Financial Collateral (Received)	(96)	(108)
Net amount, liabilities	$ (9)	$ (16)