Condensed Financial Information of the Parent Company - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	$ 732	$ 678
Short-term investments	1,272	2,562
Securities available for sale	21,843	19,428
Total loans	93,746	88,669
Goodwill	2,664	2,516	$ 2,538
Corporate-owned life insurance	4,233	4,171
Derivative assets	780	531
Accrued income and other assets	5,494	5,030
Total assets	144,988	139,613
Accrued expense and other liabilities	2,540	2,113
Total long-term debt	12,448	13,732
Total liabilities	127,950	124,017
SHAREHOLDERS' EQUITY	17,038	15,595
Total liabilities and equity	144,988	139,613
Key [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and due from banks	3,813	3,241
Short-term investments	20	19
Securities available for sale	10	10
Other investments	36	31
Total loans	66	81
Total investment in subsidiaries	17,792	16,387
Goodwill	167	167
Corporate-owned life insurance	205	199
Derivative assets	44	61
Accrued income and other assets	295	279
Total assets	22,448	20,475
Accrued expense and other liabilities	492	480
Long term debt due to Subsidiaries	483	471
Total long-term debt	4,918	4,400
Total liabilities	5,410	4,880
SHAREHOLDERS' EQUITY	17,038	15,595
Total liabilities and equity	22,448	20,475
Key [Member] | Banks [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	50	50
Investment in subsidiaries	16,969	15,554
Key [Member] | Nonbank Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Total loans	16	31
Investment in subsidiaries	823	833
Key [Member] | Unaffiliated Companies [Member]
Condensed Financial Statements, Captions [Line Items]
Total long-term debt	$ 4,435	$ 3,929