Segment Reporting (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) employee	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) employee segment
Segment Reporting [Abstract]
Number of Reportable Segments | segment			3
Income Statement Related Disclosures [Abstract]
Net interest income	$ 373,260	$ 397,175
Non-interest revenue	103,857	79,378
Non-interest expense	276,279	292,410
Pre-provision net revenue	200,838
Balance Sheet Related Disclosures [Abstract]
Loans, net of deferred fees and costs	38,258,024		$ 37,162,450
Total deposits	$ 39,826,585		$ 38,405,504
Total full-time equivalent employees | employee	5,302,000		5,264,000
Operating Segments | Community Banking
Income Statement Related Disclosures [Abstract]
Net interest income	$ 197,246
Non-interest revenue	33,449
Non-interest expense	75,304
Pre-provision net revenue	155,391
Balance Sheet Related Disclosures [Abstract]
Loans, net of deferred fees and costs	12,224,112		$ 12,170,914
Total deposits	$ 25,364,034		$ 25,610,777
Total full-time equivalent employees | employee	2,291,000		2,301,000
Operating Segments | Wholesale Banking
Income Statement Related Disclosures [Abstract]
Net interest income	$ 123,170
Non-interest revenue	9,256
Non-interest expense	18,202
Pre-provision net revenue	114,224
Balance Sheet Related Disclosures [Abstract]
Loans, net of deferred fees and costs	18,691,302		$ 17,643,509
Total deposits	$ 9,111,207		$ 8,314,184
Total full-time equivalent employees | employee	237,000		213,000
Operating Segments | Financial Management Services
Income Statement Related Disclosures [Abstract]
Net interest income	$ 16,782
Non-interest revenue	47,275
Non-interest expense	43,289
Pre-provision net revenue	20,768
Balance Sheet Related Disclosures [Abstract]
Loans, net of deferred fees and costs	5,344,276		$ 5,285,455
Total deposits	$ 266,839		$ 284,716
Total full-time equivalent employees | employee	838,000		839,000
Treasury and Corporate Other
Income Statement Related Disclosures [Abstract]
Net interest income	$ 36,062
Non-interest revenue	13,877
Non-interest expense	139,484
Pre-provision net revenue	(89,545)
Balance Sheet Related Disclosures [Abstract]
Loans, net of deferred fees and costs	1,998,334		$ 2,062,572
Total deposits	$ 5,084,505		$ 4,195,827
Total full-time equivalent employees | employee	1,936,000		1,911,000
Proforma
Income Statement Related Disclosures [Abstract]
Net interest income		397,175
Non-interest revenue		79,378
Non-interest expense		292,410
Pre-provision net revenue		184,143
Proforma | Operating Segments | Community Banking
Income Statement Related Disclosures [Abstract]
Net interest income		214,759
Non-interest revenue		32,776
Non-interest expense		74,816
Pre-provision net revenue		172,719
Proforma | Operating Segments | Wholesale Banking
Income Statement Related Disclosures [Abstract]
Net interest income		125,611
Non-interest revenue		6,758
Non-interest expense		15,019
Pre-provision net revenue		117,350
Proforma | Operating Segments | Financial Management Services
Income Statement Related Disclosures [Abstract]
Net interest income		28,865
Non-interest revenue		32,279
Non-interest expense		33,218
Pre-provision net revenue		27,926
Proforma | Treasury and Corporate Other
Income Statement Related Disclosures [Abstract]
Net interest income		27,940
Non-interest revenue		7,565
Non-interest expense		169,357
Pre-provision net revenue		$ (133,852)