Fair Value (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	$ 1,000,000	$ 2,000,000	$ 1,000,000	$ 4,000,000
Private equity investments carried at cost	8,000,000		8,000,000		$ 8,000,000
Federal Reserve and Federal Home Loan Bank stock	108,000,000		108,000,000		157,000,000
Private equity investments accounted for under the equity method	50,000,000		50,000,000		$ 45,000,000
Level 3
Derivatives, Fair Value [Line Items]
Realized gains (losses) in the statement of income	0	(9,000,000)	15,000,000	(9,000,000)
Other real estate owned properties
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	1,000,000	2,000,000	1,000,000	3,000,000
Carrying value of OREO properties	$ 3,000,000	$ 4,000,000	$ 3,000,000	$ 4,000,000