Derivative Instruments - Derivatives - Offsetting Derivative Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Asset Derivatives	$ 35	$ 31
Derivative assets	12	7
Accrued Interest and Cash Collateral (Received)	(1)	(4)
Gross Amounts of Recognized (Liabilities)	(94)	(92)
Derivative Liability	(71)	(68)
Other liabilities
Derivative [Line Items]
Accrued Interest and Cash Collateral (Received)	11	4
Gross Amounts of Recognized (Liabilities)	(94)	(92)
Gross Amounts Offset in the Statement of Financial Position, liabilities	(12)	(20)
Derivative Liability	(71)	(68)
Financial Collateral (Received)	(73)	(65)
Net amount, liabilities	(9)	(7)
Other investments
Derivative [Line Items]
Asset Derivatives	35	31
Gross Amounts Offset in the Statement of Financial Position, assets	32	26
Derivative assets	12	7
Accrued Interest and Cash Collateral (Received)	9	2
Financial Collateral Pledged	1	2
Net Amount, assets	$ 2	$ 3