Derivative Instruments - Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Asset Derivatives	$ 47	$ 40
Derivative assets	10	12
Gross Amounts of Recognized (Liabilities)	(103)	(106)
Derivative Liability	(66)	(78)
Other liabilities
Derivative [Line Items]
Derivative, Collateral, Obligation to Return Cash	24	5
Gross Amounts of Recognized (Liabilities)	(103)	(106)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(13)	(23)
Derivative Liability	(66)	(78)
Derivative, Collateral, Obligation to Return Cash	(24)	(5)
Financial Collateral (Received)	(81)	(73)
Net amount, liabilities	(9)	(10)
Other investments
Derivative [Line Items]
Asset Derivatives	47	40
Gross Amounts Offset in the Statement of Financial Position, assets	43	37
Derivative assets	10	12
Derivative, Collateral, Obligation to Return Cash	6	9
Financial Collateral Pledged	2	1
Net Amount, assets	2	2
Derivative, Collateral, Obligation to Return Cash	$ (6)	$ (9)