Quarterly report pursuant to Section 13 or 15(d)

Components of Net Periodic Benefit Cost (Detail)

v2.4.0.6
Components of Net Periodic Benefit Cost (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Pension Benefits [Member]
       
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 1.6 $ 1.6 $ 4.8 $ 4.8
Interest cost 8.3 8.6 24.9 25.8
Expected return on plan assets (11.6) (11.6) (34.8) (34.9)
Amortization of prior service cost 0.2 0.2 0.6 0.6
Recognized actuarial loss 4.0 3.0 12.0 9.0
Total net periodic benefit cost 2.5 1.8 7.5 5.3
Other Benefits [Member]
       
Defined Benefit Plan Disclosure [Line Items]        
Service cost 0.1 0.1 0.3 0.4
Interest cost 0.3 0.4 0.9 1.2
Expected return on plan assets (0.4) (0.4) (1.2) (1.2)
Amortization of prior service cost (0.1) 0 (0.3) (0.1)
Recognized actuarial loss 0.3 0.3 0.9 0.9
Total net periodic benefit cost $ 0.2 $ 0.4 $ 0.6 $ 1.2