Derivatives - Derivative Liabilities and Collateral Pledged (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Gross amounts of recognized liabilities	$ 125	$ 44
Gross  amounts offset in the Balance Sheets	0	0
Net amounts of liabilities presented in the Statements of Condition	125	44
Derivative assets available for offset	(21)	(19)
Collateral pledged	(82)	(25)
Net amount	22	0
Derivative liabilities not subject to master netting agreements	22	23
Derivatives, interest rate contracts
Derivative [Line Items]
Gross amounts of recognized liabilities	60	24
Gross  amounts offset in the Balance Sheets	0	0
Net amounts of liabilities presented in the Statements of Condition	60	24
Derivative assets available for offset	(7)	(6)
Collateral pledged	(31)	(18)
Net amount	22	0
Forward contracts
Derivative [Line Items]
Gross amounts of recognized liabilities	65	20
Gross  amounts offset in the Balance Sheets	0	0
Net amounts of liabilities presented in the Statements of Condition	65	20
Derivative assets available for offset	(14)	(13)
Collateral pledged	(51)	(7)
Net amount	$ 0	$ 0