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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at statutory rate	$ 368	$ 409	$ 821	$ 820
State income tax, at statutory rates, net of federal tax benefit	83	84	185	168
Tax credits and benefits, net of related expenses	(63)	(46)	(140)	(152)
Tax-exempt income	(41)	(29)	(75)	(57)
Other items	35	(4)	46	32
Applicable income taxes	$ 382	$ 414	$ 837	$ 811