Condensed Financial Information of the Parent Company - Condensed Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	$ 677	$ 607	$ 653	$ 617
Short-term investments	2,775	2,707
Securities available for sale	20,212	14,218
Other investments	738	655
Total loans	85,180	59,080
Goodwill	2,446	1,060	1,057
Other intangible assets	384	65
Corporate-owned life insurance	4,068	3,541
Derivative assets	803	619
Accrued income and other assets	3,864	3,290
Total assets	136,453	95,131
Accrued expense and other liabilities	1,796	1,605
Derivative liabilities	636	632
Total long-term debt	12,384	10,184
Total liabilities	121,213	84,372
SHAREHOLDERS' EQUITY	15,240	10,746
Total liabilities and equity	136,453	95,131
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	3,286	2,608	$ 2,207	$ 2,418
Short-term investments	70	58
Securities available for sale	10	10
Other investments	25	14
Total loans	281	437
Total investment in subsidiaries	15,232	10,658
Goodwill	167	167
Other intangible assets	0	0
Corporate-owned life insurance	207	206
Derivative assets	53	12
Accrued income and other assets	451	319
Total assets	19,782	14,489
Accrued expense and other liabilities	553	503
Derivative liabilities	2	0
Long term debt due to Subsidiaries	850	423
Total long-term debt	3,987	3,240
Total liabilities	4,542	3,743
SHAREHOLDERS' EQUITY	15,240	10,746
Total liabilities and equity	19,782	14,489
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	250	250
Investment in subsidiaries	14,564	9,955
Key [Member] | Nonbank Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	31	187
Investment in subsidiaries	668	703
Key [Member] | Unaffiliated Companies [Member]
Condensed Financial Statements, Captions [Line Items]
Total long-term debt	$ 3,137	$ 2,817