Derivative Financial Instruments and Off-balance sheet Financial Instruments - Gross and net amounts for OTC derivatives (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Asset derivatives
Gross amount	$ 218	$ 142
Derivative asset, counterparty netting	(12)	0
Net amount on balance sheet	206	142
Liability derivatives
Gross amount	(657)	(546)
Derivative liability, counterparty netting	2	39
Net amount on balance sheet	(655)	(507)
OTC derivatives
Asset derivatives
Gross amount	16	40
Derivative asset, counterparty netting	(14)	(39)
Derivative asset, cash collateral (received) pledged	(1)	(1)
Net amount on balance sheet	1	0
Securities collateral (received) pledged	0	0
Net amount	1	0
Liability derivatives
Gross amount	(28)	(16)
Derivative liability, counterparty netting	14	39
Derivative liability, cash collateral (received) pledged	13	(27)
Net amount on balance sheet	(1)	(4)
Securities collateral (received) pledged	0	0
Net amount	$ (1)	$ (4)