Capital Structure - Narrative (Details) - USD ($)						6 Months Ended
	Jun. 15, 2023	May 18, 2023	Apr. 17, 2023	Mar. 31, 2023	Mar. 29, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt outstanding:
Preferred stock, par value (in dollars per share)						$ 1	$ 1
Redemption of preferred stock			$ 575,000,000
Preferred stock, shares issued (in shares)						82,000	81,000
Series G Noncumulative Preferred Stock
Debt outstanding:
Stock redeemed (in shares)			23,000
Preferred stock, par value (in dollars per share)			$ 1.00
Liquidation preference amount (in dollars per shares)			$ 25,000
Preferred stock dividends			$ 18,000,000
Series J Noncumulative Preferred Stock
Debt outstanding:
Preferred stock, par value (in dollars per share)		$ 1.00
Liquidation preference amount (in dollars per shares)		$ 25,000
Preferred stock, shares issued (in shares)		24,000
Gross proceeds		$ 600,000,000
Preferred stock, redemption price par value (in dollars per share)		$ 25,000
Period after occurrence of certain tax and rating agency events in which redemption of debt in whole permissible		90 days
Series J Noncumulative Preferred Stock | Preferred Stock, Redemption, Period Three
Debt outstanding:
Preferred stock, redemption price par value (in dollars per share)		$ 25,000
Series J Noncumulative Preferred Stock | Preferred Stock, Redemption, Period One
Debt outstanding:
Preferred stock, redemption price par value (in dollars per share)		$ 25,500
Series J Noncumulative Preferred Stock | Preferred Stock, Redemption, Period Two
Debt outstanding:
Number of days after regulatory capital event		90 days
Senior Notes
Debt outstanding:
Repayments of debt	$ 500,000,000			$ 500,000,000	$ 250,000,000
Senior Notes | Senior Notes Due 2033 at 5.25 Percent
Debt outstanding:
Issuance of debt				$ 750,000,000
Subsequent acquisition (in percentage)				5.25%
Senior Notes | London Interbank Offered Rate
Debt outstanding:
Basis spread on interest at floating rate	3.15%				0.63%
5.100% Fixed-to-Floating Rate Subordinated Debentures due 2053
Debt outstanding:
Subsequent acquisition (in percentage)						5.10%
5.100% Fixed-to-Floating Rate Subordinated Debentures due 2053 | London Interbank Offered Rate
Debt outstanding:
Basis spread on interest at floating rate						3.165%
5.750% Subordinated Debentures, due 2053
Debt outstanding:
Subsequent acquisition (in percentage)						5.75%
5.750% Subordinated Debentures, due 2053 | London Interbank Offered Rate
Debt outstanding:
Basis spread on interest at floating rate						2.938%
Subordinated Debt
Debt outstanding:
Maximum period for deferment of interest payment						5 years
Subordinated Debt | Secured Overnight Financing Rate (SOFR)
Debt outstanding:
Basis spread on interest at floating rate						0.26161%