Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of cash and cash equivalents and other investments reconciliation from adjusted cost to fair value

Our cash and cash equivalents and other investments consist of the following:

	March 31, 2015
	Cost Basis		Unrealized Gains		Unrealized Losses		Fair Value
	(in millions)
Cash	$	62.4	$	—	$	—	$	62.4
Cash equivalents:
U.S. and Canadian government obligations	1,691.4		—		—		1,691.4
Other debt securities	25.0		—		—		25.0
Total cash and cash equivalents	$	1,778.8	$	—	$	—	$	1,778.8
Restricted cash	63.3		—		—		63.3
Nonqualified employee benefit trusts	18.4		2.1		—		20.5

	December 31, 2014
	Cost Basis		Unrealized Gains		Unrealized Losses		Fair Value
	(in millions)
Cash	$	71.3	$	—	$	—	$	71.3
Cash equivalents:
U.S. and Canadian government obligations	1,916.3		—		—		1,916.3
Other debt securities	9.0		—		—		9.0
Total cash and cash equivalents	$	1,996.6	$	—	$	—	$	1,996.6
Restricted cash	86.1		—		—		86.1
Nonqualified employee benefit trusts	17.4		2.0		—		19.4

Schedule of assets and liabilities measured at fair value on a recurring basis

The following tables present assets and liabilities included in our consolidated balance sheets as of March 31, 2015 and December 31, 2014 that are recognized at fair value on a recurring basis, and indicate the fair value hierarchy utilized to determine such fair value:

	March 31, 2015
	Total Fair Value			Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
	(in millions)
Cash equivalents	$	1,716.4		$	1,716.4	$	—		$	—
Restricted cash	63.3			63.3		—			—
Derivative assets	6.2			—		6.2			—
Nonqualified employee benefit trusts	20.5			20.5		—			—
Derivative liabilities	(43.5		)	—		(43.5		)	—

	December 31, 2014
	Total Fair Value			Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
	(in millions)
Cash equivalents	$	1,925.3		$	1,925.3	$	—		$	—
Restricted cash	86.1			86.1		—			—
Derivative assets	0.5			—		0.5			—
Nonqualified employee benefit trusts	19.4			19.4		—			—
Derivative liabilities	(48.4		)	—		(48.4		)	—

Schedule of carrying amounts and estimated fair values of financial instruments

The carrying amounts and estimated fair values of our financial instruments are as follows:

	March 31, 2015				December 31, 2014
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
	(in millions)
Long-term debt	$	4,592.5	$	5,086.6	$	4,592.5	$	4,969.3