Allowances for Credit Losses and Recorded Investments in Loans and Leases by Segment (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	$ 303.1		$ 269.8
Evaluated for Inherent Impairment	28,507.3		29,234.7
Total Loans and Leases	28,810.4		29,504.5
Specifically Evaluated for Impairment	18.4		18.0
Evaluated for Inherent Impairment	272.0		279.9
Allowance Assigned to Loans and Leases	290.4		297.9
Allowance for Unfunded Exposures Commitments and Standby Letters of Credit	30.3		29.7
Total Allowance for Credit Losses	320.7	323.8	327.6	329.9	328.1	328.9
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	113.9		125.0
Evaluated for Inherent Impairment	12,505.7		12,772.2
Total Loans and Leases	12,619.6		12,897.2
Specifically Evaluated for Impairment	14.5		11.0
Evaluated for Inherent Impairment	142.1		155.1
Allowance Assigned to Loans and Leases	156.6		166.1
Allowance for Unfunded Exposures Commitments and Standby Letters of Credit	27.5		28.1
Total Allowance for Credit Losses	184.1	187.1	194.2	196.3	202.0	211.0
Personal
Financing Receivable, Allowance for Credit Losses [Line Items]
Specifically Evaluated for Impairment	189.2		144.8
Evaluated for Inherent Impairment	16,001.6		16,462.5
Total Loans and Leases	16,190.8		16,607.3
Specifically Evaluated for Impairment	3.9		7.0
Evaluated for Inherent Impairment	129.9		124.8
Allowance Assigned to Loans and Leases	133.8		131.8
Allowance for Unfunded Exposures Commitments and Standby Letters of Credit	2.8		1.6
Total Allowance for Credit Losses	$ 136.6	$ 136.7	$ 133.4	$ 133.6	$ 126.1	$ 117.9