Income Taxes - Reconciliation of Expected Income Tax Expense at Federal Statutory Rate of 35 Percent to Company's Applicable Income Tax Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 668	$ 681
State income tax, at statutory rates, net of federal tax benefit	43	36
Tax effect of
Tax credits and benefits, net of related expenses	(165)	(106)
Tax-exempt income	(52)	(54)
Noncontrolling interests	(5)	14
Other items	7	(13)
Applicable income taxes	$ 496	$ 558