Condensed Financial Information of the Parent Company - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	$ 678	$ 671	$ 677	$ 607
Short-term investments	2,562	4,447
Securities available for sale	19,428	18,139
Other investments	666	726
Total loans	88,669	85,528
Goodwill	2,516	2,538	2,446
Corporate-owned life insurance	4,171	4,132
Derivative assets	531	669
Accrued income and other assets	4,037	4,237
Total assets	139,613	137,698
Accrued expense and other liabilities	2,113	2,094
Total long-term debt	13,732	14,333
Total liabilities	124,017	122,673
SHAREHOLDERS' EQUITY	15,595	15,023
Total liabilities and equity	139,613	137,698
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	3,241	2,257	$ 3,286	$ 2,608
Short-term investments	19	22
Securities available for sale	10	10
Other investments	31	29
Total loans	81	281
Total investment in subsidiaries	16,387	16,054
Goodwill	167	167
Corporate-owned life insurance	199	208
Derivative assets	61	29
Accrued income and other assets	279	353
Total assets	20,475	19,410
Accrued expense and other liabilities	480	466
Long term debt due to Subsidiaries	471	480
Total long-term debt	4,400	3,921
Total liabilities	4,880	4,387
SHAREHOLDERS' EQUITY	15,595	15,023
Total liabilities and equity	20,475	19,410
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	50	250
Investment in subsidiaries	15,554	15,169
Key [Member] | Nonbank Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	31	31
Investment in subsidiaries	833	885
Key [Member] | Unaffiliated Companies [Member]
Condensed Financial Statements, Captions [Line Items]
Total long-term debt	$ 3,929	$ 3,441