Debt and Credit Facilities - Lines of Credit (Parenthetical) (Detail) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Line Of Credit Facility [Line Items]
Cash held on deposit as compensating balance		$ 26.3	$ 25.4
Total available lines of credit	[1]	1,123.0	$ 1,157.4
Committed Line of Credit Facilities [Member]
Line Of Credit Facility [Line Items]
Total available lines of credit		$ 869.8

[1] Of the total available lines of credit, $869.8 million were committed as of March 31, 2017.