Items Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	$ 0.5	$ 3.2
Total assets	118.2	117.5
Derivative liabilities	44.3	37.0
Total liabilities	49.5	39.5
Bank time deposits with original maturities of three months or less
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank time deposits with original maturities of three months or less	112.5	111.8
Diversified investments associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Diversified investments associated with the ESUP	5.2	2.5
Liabilities associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities	5.2	2.5
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	5.2	2.5
Derivative liabilities	1.5	2.2
Total liabilities	6.7	4.7
Level 1 | Diversified investments associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Diversified investments associated with the ESUP	5.2	2.5
Level 1 | Liabilities associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities	5.2	2.5
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0.5	3.2
Total assets	113.0	115.0
Derivative liabilities	42.8	34.8
Total liabilities	42.8	34.8
Level 2 | Bank time deposits with original maturities of three months or less
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Bank time deposits with original maturities of three months or less	112.5	111.8
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 3 | Diversified investments associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Diversified investments associated with the ESUP
Level 3 | Liabilities associated with the ESUP
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities