Employee Postretirement Benefits - Schedule of Fair Value Hierarchy Plan's Investments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 529.1	$ 467.6
Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35.3	17.8
Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	287.7	232.4
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	214.8	194.0
Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.8)	(0.2)
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	4.4
Accounts receivable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64.8	39.6
Accounts payable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(72.8)	(20.4)
Short term investment fund (STIF) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9.0	13.2
Treasury bills (T bills) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	4.3
Money markets [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	0.3
Common Stock [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	125.3	114.2
American depository receipt (ADR) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.2	7.1
Real estate investment trust (REIT) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.0	2.0
Mutual fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	153.4	88.3
Mutual fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63.7	101.1
Preferred stocks [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	1.0
Commingled fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19.8
Commingled fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49.4
Municipal bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.0	8.7
Government bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53.0	31.7
Corporate bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.8	29.5
Asset backed securities (ABS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.5
Mortgage back securities (MBS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.6	20.0
CMO [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.5	2.5
Swaps [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.5)	(0.3)
Written options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.4)	0.1
Repurchase agreements [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.1
Certificates of Deposit [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.1
Commercial Paper [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9
Commercial Mortgage Backed Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3
Purchased Options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1
Miscellaneous [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	287.9	247.8
Level 1 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9.0	13.2
Level 1 [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	286.9	211.0
Level 1 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	4.4
Level 1 [Member] | Accounts receivable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64.8	39.6
Level 1 [Member] | Accounts payable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(72.8)	(20.4)
Level 1 [Member] | Short term investment fund (STIF) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9.0	13.2
Level 1 [Member] | Treasury bills (T bills) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Money markets [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Common Stock [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	125.3	114.2
Level 1 [Member] | American depository receipt (ADR) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.2	6.5
Level 1 [Member] | Real estate investment trust (REIT) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.0	2.0
Level 1 [Member] | Mutual fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	153.4	88.3
Level 1 [Member] | Mutual fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Preferred stocks [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Commingled fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Level 1 [Member] | Commingled fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Municipal bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Government bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Corporate bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Asset backed securities (ABS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Mortgage back securities (MBS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | CMO [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Swaps [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Written options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 1 [Member] | Repurchase agreements [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Certificates of Deposit [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Commercial Paper [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Commercial Mortgage Backed Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Purchased Options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 1 [Member] | Miscellaneous [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	241.2	219.8
Level 2 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	26.3	4.6
Level 2 [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	21.4
Level 2 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	214.8	194.0
Level 2 [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.8)	(0.2)
Level 2 [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Accounts receivable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Accounts payable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Short term investment fund (STIF) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Treasury bills (T bills) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	4.3
Level 2 [Member] | Money markets [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.6	0.3
Level 2 [Member] | Common Stock [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | American depository receipt (ADR) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0.6
Level 2 [Member] | Real estate investment trust (REIT) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Mutual fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 2 [Member] | Mutual fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63.7	101.1
Level 2 [Member] | Preferred stocks [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	1.0
Level 2 [Member] | Commingled fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19.8
Level 2 [Member] | Commingled fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49.4
Level 2 [Member] | Municipal bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.0	8.7
Level 2 [Member] | Government bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53.0	31.7
Level 2 [Member] | Corporate bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.8	29.5
Level 2 [Member] | Asset backed securities (ABS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	0.5
Level 2 [Member] | Mortgage back securities (MBS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.6	20.0
Level 2 [Member] | CMO [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.5	2.5
Level 2 [Member] | Swaps [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.5)	(0.3)
Level 2 [Member] | Written options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.4)	0.1
Level 2 [Member] | Repurchase agreements [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23.1
Level 2 [Member] | Certificates of Deposit [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.1
Level 2 [Member] | Commercial Paper [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.9
Level 2 [Member] | Commercial Mortgage Backed Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3
Level 2 [Member] | Purchased Options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1
Level 2 [Member] | Miscellaneous [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Accounts receivable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Accounts payable [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Short term investment fund (STIF) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Treasury bills (T bills) [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Money markets [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Common Stock [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | American depository receipt (ADR) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Real estate investment trust (REIT) [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Mutual fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Mutual fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Preferred stocks [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Commingled fund [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Level 3 [Member] | Commingled fund [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Municipal bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Government bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Corporate bonds [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Asset backed securities (ABS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Mortgage back securities (MBS) [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | CMO [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Swaps [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Written options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 [Member] | Repurchase agreements [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Certificates of Deposit [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Commercial Paper [Member] | Cash equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Commercial Mortgage Backed Securities [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Purchased Options [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Level 3 [Member] | Miscellaneous [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0