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
	Mar. 31, 2023	Mar. 31, 2022
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at statutory rate	$ 453	$ 411
State income tax, at statutory rates, net of federal tax benefit	102	84
Tax credits and benefits, net of related expenses	(77)	(106)
Tax-exempt income	(34)	(28)
Other items	11	36
Applicable income taxes	$ 455	$ 397