Other Securities - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Banking and Thrift, Interest [Abstract]
Federal Home Loan Bank stock	$ 154,000,000	$ 256,000,000
Federal Reserve Bank stock	124,000,000	123,000,000
Other non-marketable equity securities	0	1,000,000
Total non-marketable equity securities	278,000,000	380,000,000
Other non-marketable equity securities, impairment	$ 0	$ 0