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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at statutory rate	$ 482	$ 546	$ 1,302	$ 1,686
State income tax, at statutory rates, net of federal tax benefit	91	108	259	327
Tax credits and benefits, net of related expenses	(79)	(91)	(231)	(267)
Tax-exempt income	(30)	(28)	(87)	(85)
Other items	17	29	49	61
Applicable income taxes	$ 481	$ 564	$ 1,292	$ 1,722