Securities Financing Activities - Summarized Securities Financing Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	$ 0	$ 0
Total offsetting of financial assets	0	0
Repurchase agreements	0	0
Total offsetting of financial liabilities	0	0
Counterparty And Cash Collateral Netting [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	0	0
Total offsetting of financial assets	0	0
Repurchase agreements	(180)	(305)
Total offsetting of financial liabilities	(180)	(305)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities Financing Transaction [Line Items]
Carrying amount of assets pledged as collateral against repurchase agreements	204
Liabilities associated with collateral pledged	180
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	5	14
Total offsetting of financial assets	5	14
Repurchase agreements	187	319
Total offsetting of financial liabilities	187	319
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(5)	(14)
Total offsetting of financial assets	(5)	(14)
Repurchase agreements	(7)	(14)
Total offsetting of financial liabilities	$ (7)	$ (14)