Fair Value Measurements - Commodity and Foreign Currency Contracts (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Fair value measurement, additional disclosure
Cash collateral deposits held by financial counterparties		$ 54.7	$ 174.6
Cash collateral deposits held by financial counterparties, offset against liabilities		12.4	132.2
Cash collateral deposits held by financial counterparties, not offset		42.3	42.4
Cash collateral received from customers		4.2	21.6
Commodity contracts
Derivative instruments, at their respective fair value positions
Total net assets	[1]	50.1	231.5
Total net liabilities	[1]	41.7	74.1
Commodity contracts | Short-term derivative assets, net
Derivative instruments, at their respective fair value positions
Total net assets	[1]	37.3	212.6
Commodity contracts | Identifiable intangible and other non-current assets
Derivative instruments, at their respective fair value positions
Total net assets	[1]	12.8	18.9
Commodity contracts | Accrued expenses and other current liabilities
Derivative instruments, at their respective fair value positions
Total net liabilities	[1]	34.2	68.7
Commodity contracts | Other long-term liabilities
Derivative instruments, at their respective fair value positions
Total net liabilities	[1]	7.5	5.4
Foreign currency contracts
Derivative instruments, at their respective fair value positions
Total net assets	[1]	8.5	8.3
Total net liabilities	[1]	1.8	0.9
Foreign currency contracts | Short-term derivative assets, net
Derivative instruments, at their respective fair value positions
Total net assets	[1]	6.9	7.6
Total net liabilities	[1]	1.8	0.9
Foreign currency contracts | Identifiable intangible and other non-current assets
Derivative instruments, at their respective fair value positions
Total net assets	[1]	$ 1.6	$ 0.7

[1] Amounts may not add due to rounding