Derivative Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Asset derivatives
Asset derivatives gross amount	$ 243	$ 218
Asset derivatives, gross liability	(15)	(12)
Derivative assets net amount on balance sheet	228	206
Liability derivatives
Liability derivatives gross amount	(626)	(657)
Liability derivatives, gross asset	2	2
Net amount on balance sheet	(624)	(655)
OTC derivatives
Asset derivatives
Asset derivatives gross amount	17	10
Asset derivatives, gross liability	(13)	(9)
Cash collateral received	(1)	0
Derivative assets net amount on balance sheet	3	1
Derivative assets received under securities collateral	0	0
Derivative asset, fair value, amount offset against collateral	3	1
Liability derivatives
Liability derivatives gross amount	(13)	(19)
Liability derivatives, gross asset	13	9
Derivative liability offsets under cash collateral pledged	0	9
Net amount on balance sheet	0	(1)
Derivative liabilities received under securities collateral	0	0
Derivative liability, fair value, amount offset against collateral	$ 0	$ (1)