CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Trading investments, cost	$ 29,049	$ 12,551
Available-for-sale investments, cost	2,506,087	1,986,957
Allowance for credit losses on loans and leases	$ 1,215,407	$ 1,361,723
Preferred stock, par or stated value (in dollars per share)	$ 0.20	$ 0.20
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Preferred stock, shares outstanding (in shares)	2,500,000	2,500,000
Preferred stock, liquidation preference (in dollars per share)	$ 100	$ 100
Common stock, par value (in dollars per share)	$ 0.20	$ 0.20
Common stock, shares authorized (in shares)	1,125,000,000	1,125,000,000
Common stock, shares issued (in shares)	432,000,000.0	456,700,000
Accumulated other comprehensive income, tax	$ (6,288)	$ (10,908)
Treasury stock, shares (in shares)	138,800,000	81,400,000