Income Taxes - Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Losses on loans and other assets	$ 345,609	$ 590,288	$ 637,955
Retirement benefits	45,322	143,067	148,722
Postretirement and other employee benefits	26,009	52,512	55,962
Incentive and other compensation plans	25,050	36,616	60,337
Interest on loans	37,900	61,266	57,640
Stock-based compensation	26,676	52,181	72,090
Unrealized losses		10,741
Other	66,247	106,876	162,086
Gross deferred tax assets	572,813	1,053,547	1,194,792
Leasing transactions	(181,159)	(266,268)	(285,074)
Unrealized gains	(94,285)		(31,121)
Capitalized servicing rights	(51,781)	(71,108)	(59,171)
Depreciation and amortization	(52,733)	(63,959)	(56,731)
Other	(21,599)	(87,200)	(55,611)
Gross deferred tax liabilities	(401,557)	(488,535)	(487,708)
Net deferred tax asset	$ 171,256	$ 565,012	$ 707,084