Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities:
Net income	$ 520.4	$ 468.1	$ 337.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of premises and equipment	41.7	36.3	39.1
Expense related to operating leases	38.8	36.4	35.2
Amortization of other acquisition-related intangible assets	32.5	21.8	30.0
Provision for loan losses	28.3	30.0	26.0
Expense related to share-based awards	24.9	22.4	19.8
Deferred income tax expense	14.3	1.9	25.8
ESOP common stock committed to be released	5.7	6.2	6.4
Net security (gains) losses	(0.2)	9.8	25.4
Net gains on sales of acquired loans	(0.4)	(1.8)	(2.4)
Net gains on sales of residential mortgage loans	(1.9)	(1.2)	(3.2)
Originations of loans held-for-sale	(180.3)	(188.2)	(261.8)
Proceeds from sales of loans held-for-sale	181.9	186.5	287.7
Net changes in trading debt securities	1.3	(0.2)	(1.4)
Excess income tax benefits from stock options exercised	0.3	1.3	1.1
Net changes in other assets and other liabilities	(466.5)	(40.0)	38.1
Net cash provided by operating activities	240.8	589.3	603.0
Cash Flows from Investing Activities:
Proceeds from sales of equity securities	1.6	2.3	0.0
Proceeds from principal repayments and maturities of debt securities available-for-sale	578.5	465.5	562.6
Proceeds from sales of debt securities available-for-sale	365.3	313.8	1,305.5
Proceeds from principal repayments and maturities of debt securities held-to-maturity	158.2	185.3	120.9
Purchases of debt securities available-for-sale	(827.8)	(726.8)	(603.3)
Purchases of debt securities held-to-maturity	(257.9)	(407.4)	(1,580.4)
Net redemptions of Federal Home Loan Bank stock	19.3	17.2	27.1
Net purchases of Federal Reserve Bank stock	(25.2)	(8.3)	(20.8)
Proceeds from sales of loans	51.2	22.3	38.7
Net principal (disbursements) collections of loans	(770.3)	244.8	(538.7)
Purchases of loans	(71.2)	(37.5)	(17.7)
Purchases of premises and equipment	(26.5)	(28.3)	(4.8)
Purchases of leased equipment, net	(41.2)	(59.6)	(24.2)
Proceeds from sales of real estate owned	13.9	9.1	10.0
Return of premiums on bank-owned life insurance, net	2.2	1.0	2.7
Net cash acquired in acquisitions and dispositions	519.4	6.2	28.9
Net cash used in investing activities	(310.5)	(0.4)	(693.5)
Cash Flows from Financing Activities:
Net (decrease) increase in deposits	(117.6)	696.6	1,343.1
Net increase (decrease) in borrowings with terms of three months or less	647.7	(525.7)	(293.8)
Repayments of borrowings with terms of more than three months	(321.2)	(476.7)	(380.7)
Repayments of notes and debentures	0.0	0.0	(125.0)
Cash dividends paid on common stock	(274.8)	(243.8)	(227.9)
Cash dividends paid on preferred stock	(14.1)	(14.1)	(14.1)
Repurchases of common stock	(4.5)	(2.5)	(3.4)
Proceeds from stock options exercised	24.1	27.9	61.8
Contingent consideration payments	(0.9)	(1.2)	(1.0)
Net cash (used in) provided by financing activities	(61.3)	(539.5)	359.0
Net (decrease) increase in cash, cash equivalents and restricted cash	(131.0)	49.4	268.5
Cash, cash equivalents and restricted cash at beginning of year	932.0	882.6	614.1
Cash, cash equivalents and restricted cash at end of year	801.0	932.0	882.6
Supplemental Information:
Interest payments	473.4	312.3	195.9
Income tax payments	107.7	45.6	112.9
Significant non-cash transactions:
Right-of-use assets obtained in exchange for lessee operating and finance lease liabilities	91.7
Real estate properties acquired by foreclosure	19.9	7.7	17.2
Unsettled purchases of securities	0.0	4.0	0.0
Assets acquired and liabilities assumed in acquisitions and dispositions (note 2):
Non-cash assets, excluding goodwill and other acquisition-related intangibles	9,224.7	3,173.6	2,642.1
Liabilities	9,120.4	2,965.1	2,634.1
Common stock issued in acquisitions	$ 1,045.1	$ 486.4	$ 484.8