Business Combination - Additional Information (Details) $ / shares in Units, $ in Millions				3 Months Ended			6 Months Ended
		Jan. 01, 2020 USD ($)	Mar. 22, 2019 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares		Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) $ / shares		Jun. 30, 2019 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) $ / shares		Aug. 26, 2019 $ / shares shares	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) branch location
Business Acquisition [Line Items]
Total assets				$ 202,906			$ 202,906				$ 169,369
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares				$ 25,000			$ 25,000				$ 25,000
Goodwill				$ 4,261		$ 4,284	$ 4,261		$ 4,284		$ 4,252				$ 2,478
Total noninterest expense	[1]			1,121		1,243	2,321		$ 2,341
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member							us-gaap:AccountingStandardsUpdate201602Member
Allowance for loan and lease losses		$ 33		2,696	[2]	1,115	2,696	[2]	$ 1,115	$ 2,348	$ 1,202	[2]		$ 1,115	$ 1,103
Unpaid principal balance as noncredit discount		$ 87
Class C Preferred stock
Business Acquisition [Line Items]
Fixed dividend rate (as a percent)			6.00%
Class B Preferred stock, Series A
Business Acquisition [Line Items]
Fixed dividend rate (as a percent)													6.00%
Preferred stock, issued (in shares) | shares													200,000
Preferred stock, liquidation preference per share (in dollars per share) | $ / shares													$ 1,000
MB Financial, Inc.
Business Acquisition [Line Items]
Total consideration paid			$ 3,608
Total assets			$ 20,000
Full-service banking centers | branch															86
Number of locations | location															91
Percentage of common stock acquired			100.00%
Share consideration transferred | shares			1.45
Cash consideration transferred per share (in dollars per share) | $ / shares			$ 5.54
Total value per share (in dollars per share) | $ / shares			42.49
Closing price of common stock (in dollars per share) | $ / shares			$ 25.48
Fair value of noncontrolling interest in acquiree			$ 197
Percentage of voting equity interest			95.00%
Goodwill			$ 1,786
Tax deductible goodwill			$ 15
Tax deductible goodwill, period			15 years
Total noninterest expense				$ 9		$ 109	$ 16		$ 185
Contractual balances on the purchased non credit impaired loans and leases			$ 12,700
Fair value of the purchased non credit impaired loans and leases			$ 12,500

[1] During the first quarter of 2020, certain noninterest income and noninterest expense line items were reclassified to better align disclosures to business activities. These reclassifications were retrospectively applied to all prior periods presented. Total noninterest income and noninterest expense did not change as a result of these reclassifications.

[2] Includes $66 and $74 of other short-term investments, $1,032 and $1,354 of portfolio loans and leases, $(14) and $(7) of ALLL, $7 and $8 of other assets, $2 and $2 of other liabilities, and $933 and $1,253 of long-term debt from consolidated VIEs that are included in their respective captions above at June 30, 2020 and December 31, 2019, respectively. For further information refer to Note 13.