Income Taxes - Reconciliation of Expected Income Tax Expense at Federal Statutory Rate of 21 Percent to Company's Applicable Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at statutory rate	$ 411	$ 482	$ 1,232	$ 1,302
State income tax, at statutory rates, net of federal tax benefit	85	91	270	259
Tax credits and benefits, net of related expenses	(96)	(79)	(236)	(231)
Tax-exempt income	(40)	(30)	(115)	(87)
Other items	71	17	117	49
Applicable income taxes	$ 431	$ 481	$ 1,268	$ 1,292