Pensions and Other Postretirement Benefits OPEB Changes in Assets Measured at Fair Value Using Signficant Unobservale Inputs (Detail) (Fair Value, Inputs, Level 3 [Member], Defined Benefit Postretirement Life Insurance [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Inputs, Level 3 [Member] | Defined Benefit Postretirement Life Insurance [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Beginning of Year	$ 11.7	$ 11.9
Actual Return on Plan Assets Held at Year End	0.3	0.2
Plan Participant Contributions	16.2	14.7
Benefits and Expenses Paid	(16.7)	(15.1)
End of Year	$ 11.5	$ 11.7