Derivative Instruments - Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative assets	$ 14	$ 10
Derivative liabilities	(61)	(100)
Other liabilities | Other Investments and Other Liabilities
Derivative [Line Items]
Accrued Interest and Cash Collateral (Received)	(8)	(5)
Gross Amounts of Recognized (Liabilities)	(74)	(115)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(5)	(10)
Derivative liabilities	(61)	(100)
Financial Collateral (Received)	(61)	(96)
Net amount, liabilities	(8)	(9)
Other investments | Other Investments and Other Liabilities
Derivative [Line Items]
Asset Derivatives	27	25
Gross Amounts Offset in the Statement of Financial Position, assets	23	22
Derivative assets	14	10
Accrued Interest and Cash Collateral (Received)	(10)	(7)
Financial Collateral Pledged	2	1
Net Amount, assets	$ 2	$ 2