Parent Company Condensed Financial Statements (Condensed Statement of Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of income
Interest expense	$ 40,064	$ 36,755	$ 32,684	$ 30,547	$ 29,425	$ 26,169	$ 25,281	$ 23,968	$ 140,050	$ 104,843	$ 103,376
Compensation and employee benefits									335,291	300,115	262,193
Amortization of tax credit and other investments									87,950	83,446	36,120
Other expense									76,697	78,936	68,624
Income tax benefit	(89,229)	(42,624)	(39,355)	(58,268)	(50,403)	(13,321)	(39,632)	(37,155)	(229,476)	(140,511)	(194,044)
NET INCOME	$ 84,898	$ 132,660	$ 118,330	$ 169,736	$ 110,734	$ 110,143	$ 103,284	$ 107,516	505,624	431,677	384,677
Parent Company
Statement of income
Other income									721	610	625
Total income									259,839	100,717	713
Interest expense									5,429	5,017	4,636
Compensation and employee benefits									5,065	5,001	5,350
Amortization of tax credit and other investments									5,908	13,851	22,466
Other expense									1,257	1,218	2,399
Total expense									17,659	25,087	34,851
Income (loss) before income tax benefit and equity in undistributed income of subsidiaries									242,180	75,630	(34,138)
Income tax benefit									18,182	26,041	30,849
Undistributed earnings of subsidiaries, primarily bank									245,262	330,006	387,966
NET INCOME									505,624	431,677	384,677
Parent Company | Bank
Statement of income
Dividends from subsidiaries									255,000	100,000	0
Parent Company | Nonbank
Statement of income
Dividends from subsidiaries									$ 4,118	$ 107	$ 88