Pension and Savings Plans (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	$ 813.7	$ 769.6
Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	312.4	327.8	[1]
Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	473.5	416.5	[1]
Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	27.8	25.3
U.S. equity securities
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	339.2	340.4
U.S. equity securities | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	255.6	260.9	[1]
U.S. equity securities | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	83.6	79.5	[1]
U.S. equity securities | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
International equity securities
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	126.1	107.8
International equity securities | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	43.0	36.4	[1]
International equity securities | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	83.1	71.4	[1]
International equity securities | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
Collateralized Mortgage Backed Securities [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	115.5	98.9
Collateralized Mortgage Backed Securities [Member] | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0	[1]
Collateralized Mortgage Backed Securities [Member] | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	115.5	98.9	[1]
Collateralized Mortgage Backed Securities [Member] | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
U.S. debt securities
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	100.3	100.3
U.S. debt securities | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	5.7	17.0	[1]
U.S. debt securities | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	94.6	83.3	[1]
U.S. debt securities | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
International debt securities
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	35.4	32.0
International debt securities | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0	[1]
International debt securities | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	35.4	32.0	[1]
International debt securities | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
Corporate debt securities
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	54.9	45.8
Corporate debt securities | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0	[1]
Corporate debt securities | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	54.9	45.8	[1]
Corporate debt securities | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
Short-term investments
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	14.5	19.1
Short-term investments | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	8.1	13.5	[1]
Short-term investments | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	6.4	5.6	[1]
Short-term investments | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0
Interests in real estate
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	27.8	25.3
Interests in real estate | Level 1 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0	[1]
Interests in real estate | Level 2 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	0	0	[1]
Interests in real estate | Level 3 [Member]
Fair value of assets in the Master Trust by category and by fair value valuation hierarchy
Total assets at fair value	$ 27.8	$ 25.3		$ 47.7

[1] Certain amounts have been revised from a Level 2 to a Level 1 fair value hierarchy classification to conform to the current year presentation, which had no effect on previously reported consolidated results and was not material to the footnotes to the consolidated financial statements.