Income Taxes - Income Taxes Included in Income Statement (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal, currently payable	$ 149,000,000	$ 337,000,000	$ 288,000,000
State, currently payable	19,000,000	42,000,000	33,000,000
Total currently payable	168,000,000	379,000,000	321,000,000
Federal, deferred	13,000,000	(69,000,000)	16,000,000
State, deferred	(2,000,000)	(7,000,000)	(11,000,000)
Total deferred	11,000,000	(76,000,000)	5,000,000
Total income tax expense (benefit)	179,000,000	303,000,000	326,000,000
Income tax (benefit) expense on securities transactions	0	0	0
Equity and gross receipts based taxes assessed in lieu of income tax recorded in noninterest expense	$ 18,000,000	$ 16,000,000	$ 17,000,000