Derivative Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Asset derivatives
Asset derivatives gross amount	$ 69	$ 142
Asset derivatives, gross liability	(10)	0
Derivative assets net amount on balance sheet	59	142
Liability derivatives
Liability derivatives gross amount	(429)	(546)
Liability derivatives, gross asset	8	39
Derivative liabilities net amount on balance sheet	(421)	(507)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	56	40
Asset derivatives, gross liability	(18)	(39)
Derivative, collateral, right to reclaim cash	(35)	(1)
Derivative assets net amount on balance sheet	3	0
Derivative assets received under securities collateral	0	0
Derivative asset, fair value, amount offset against collateral	3	0
Liability derivatives
Liability derivatives gross amount	(13)	(16)
Liability derivatives, gross asset	18	39
Derivative liability offsets under cash collateral pledged	(6)	(27)
Derivative liabilities net amount on balance sheet	(1)	(4)
Derivative liabilities received under securities collateral	0	0
Derivative liability, fair value, amount offset against collateral	$ (1)	$ (4)