Allowances for Credit Losses and Recorded Investments in Loans and Leases by Segment (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	$ 270.6		$ 293.4
Evaluated for Inherent Impairment	30,427.0		29,092.1
Total Loans and Leases	30,697.6		29,385.5
Specifically Evaluated for Impairment	8.5		10.4
Evaluated for Inherent Impairment	266.7		267.7
Allowance Assigned to Loans and Leases	275.2		278.1
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	28.3		29.8
Total Allowance for Credit Losses	303.5	309.4	307.9	320.7	323.8	327.6
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	90.0		99.5
Evaluated for Inherent Impairment	13,901.4		12,520.5
Total Loans and Leases	13,991.4		12,620.0
Specifically Evaluated for Impairment	7.6		8.1
Evaluated for Inherent Impairment	135.8		132.8
Allowance Assigned to Loans and Leases	143.4		140.9
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	25.3		27.1
Total Allowance for Credit Losses	168.7	173.1	168.0	184.1	187.1	194.2
Personal
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	180.6		193.9
Evaluated for Inherent Impairment	16,525.6		16,571.6
Total Loans and Leases	16,706.2		16,765.5
Specifically Evaluated for Impairment	0.9		2.3
Evaluated for Inherent Impairment	130.9		134.9
Allowance Assigned to Loans and Leases	131.8		137.2
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	3.0		2.7
Total Allowance for Credit Losses	$ 134.8	$ 136.3	$ 139.9	$ 136.6	$ 136.7	$ 133.4