Parent Company Financial Statements - Condensed Statement of Income (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Expense
Interest on short-term borrowings	$ 292	$ 19
Interest on long-term borrowings	400	111	$ 62
Other expense	5,379	5,050	3,612
Income tax credits	(878)	(620)	(596)
Equity in undistributed income of subsidiaries
Net income	$ 2,741	$ 1,992	$ 1,859
Net income per common share
Basic	$ 15.85	$ 11.59	$ 13.81
Diluted	$ 15.79	$ 11.53	$ 13.8
Parent Company [Member]
Income
Dividends from consolidated subsidiaries	$ 2,041	$ 2,508	$ 1,025
Income (Loss) from Equity Method Investments	20	30	30
Other income	6	(7)	3
Total income	2,067	2,531	1,058
Expense
Interest on short-term borrowings		6
Interest on long-term borrowings	182	57	24
Other expense	40	50	36
Total expense	222	113	60
Income before income taxes and equity in undistributed income of subsidiaries	1,845	2,418	998
Income tax credits	49	22	6
Income before equity in undistributed income of subsidiaries	1,894	2,440	1,004
Equity in undistributed income of subsidiaries
Net income of subsidiaries	2,888	2,060	1,880
Less: dividends received	(2,041)	(2,508)	(1,025)
Equity in undistributed income of subsidiaries	847	(448)	855
Net income	$ 2,741	$ 1,992	$ 1,859
Net income per common share
Basic	$ 15.85	$ 11.59	$ 13.81
Diluted	$ 15.79	$ 11.53	$ 13.80