Pensions and Other Postretirement Benefits OPEB Changes in Assets Measured at Fair Value Using Signficant Unobservale Inputs (Detail) (USD $) In Millions, unless otherwise specified				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member] Defined Benefit Postretirement Life Insurance [Member]	Dec. 31, 2010 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	$ 1,141.4	$ 1,025.7	$ 869.4	$ 11.9	$ 11.9
Actual Return on Plan Assets Held at Year End				0.2	0.4
Plan Participant Contributions				14.7	14.5
Benefits and Expenses Paid				(15.1)	(14.9)
End of Year	$ 1,141.4	$ 1,025.7	$ 869.4	$ 11.7	$ 11.9