Securities Financing Activities - Summarized Securities Financing Agreements (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	$ 0	$ 0
Total	0	0
Repurchase agreements	0	0
Total	0	0
Counterparty And Cash Collateral Netting [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(7)	0
Total	(7)	0
Repurchase agreements	(261)	(305)
Total	(261)	(305)
Federal Agency CMOs [Member]
Securities Financing Transaction [Line Items]
Assets pledged as collateral	370
Liabilities pledged as collateral	261
Gross Amounts Presented In Balance Sheets [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	12	14
Total	12	14
Repurchase agreements	266	319
Total	266	319
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(5)	(14)
Total	(5)	(14)
Repurchase agreements	(5)	(14)
Total	$ (5)	$ (14)