Debt and Credit Facilities - Lines of Credit (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Line Of Credit Facility [Line Items]
Used lines of credit	$ 685.0	$ 81.6
Unused lines of credit	649.7	1,224.0
Total available lines of credit	1,334.7	1,305.6
Committed Line of Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Total available lines of credit	951.2	930.9
Uncommitted Line of Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Total available lines of credit	$ 383.5	$ 374.7