Derivative Instruments - Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative assets	$ 24	$ 7
Accrued Interest and Cash Collateral (Received)	(1)	(4)
Derivative Liability	(64)	(68)
Other liabilities
Derivative [Line Items]
Accrued Interest and Cash Collateral (Received)	(5)	(4)
Gross Amounts of Recognized (Liabilities)	(78)	(92)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(9)	(20)
Derivative Liability	(64)	(68)
Financial Collateral (Received)	(60)	(65)
Net amount, liabilities	(9)	(7)
Other investments
Derivative [Line Items]
Asset Derivatives	38	31
Gross Amounts Offset in the Statement of Financial Position, assets	31	26
Derivative assets	24	7
Accrued Interest and Cash Collateral (Received)	(17)	(2)
Financial Collateral Pledged	2	2
Net Amount, assets	$ 5	$ 3