Level 4~Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative assets	$ 12	$ 10
Derivative liabilities	(86)	(100)
Derivative Assets | Other Investments and Other Liabilities
Derivative [Line Items]
Asset Derivatives	499	469
Gross Amounts Offset in the Statement of Financial Position, assets	497	466
Derivative assets	12	10
Financial Collateral Pledged	2	1
Net Amount, assets	0	2
Accrued Interest and Cash Collateral (Received)	(10)	(7)
Derivative Liabilities | Other Investments and Other Liabilities
Derivative [Line Items]
Gross Amounts of Recognized (Liabilities)	(573)	(559)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(478)	(454)
Derivative liabilities	(86)	(100)
Accrued Interest and Cash Collateral (Received)	(9)	(5)
Financial Collateral (Received)	(85)	(96)
Net amount, liabilities	$ (10)	$ (9)