The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The portion of losses on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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The effective portion of losses on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Derivatives - Effect on Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain (loss) on derivative
Gains or losses that were excluded from the assessment of the effectiveness of fair value hedges	$ 0.0	$ 0.0	$ 0.0
Derivative, credit-risk related contingent features
Net liability position	63.2	111.7
Collateral posted	28.1	89.4
Additional assets required to be posted should credit-risk contingent feature be triggered	35.1	22.3
Cash flow hedges.
Gain (loss) on derivative
Amount of Loss Recognized in Accumulated Other Comprehensive Income (Effective Portion)	0.6
Amount of Gain Reclassified from Accumulated Other Comprehensive Income (Effective Portion)	0.4
Amount of Loss Recognized in Income (Ineffective Portion)	10.8
Cash flow hedges. \| Commodity contracts \| Revenue
Gain (loss) on derivative
Amount of Loss Recognized in Accumulated Other Comprehensive Income (Effective Portion)	106.2
Amount of Gain Reclassified from Accumulated Other Comprehensive Income (Effective Portion)	6.1
Amount of Loss Recognized in Income (Ineffective Portion)	28.6
Cash flow hedges. \| Commodity contracts \| Cost of revenue.
Gain (loss) on derivative
Amount of Loss Recognized in Accumulated Other Comprehensive Income (Effective Portion)	(105.6)
Amount of Gain Reclassified from Accumulated Other Comprehensive Income (Effective Portion)	(5.7)
Amount of Loss Recognized in Income (Ineffective Portion)	(17.8)
Derivatives designated as hedging instruments \| Fair value hedges
Gain (loss) on derivative
Realized and Unrealized Gain (Loss) on Hedge	86.8	132.2	2.7
Realized and Unrealized Gain (Loss) on Hedged Item	(70.7)	(150.9)	3.1
Derivatives designated as hedging instruments \| Fair value hedges \| Commodity contracts two \| Revenue
Gain (loss) on derivative
Realized and Unrealized Gain (Loss) on Hedge	49.3
Derivatives designated as hedging instruments \| Fair value hedges \| Commodity contracts two \| Cost of revenue.
Gain (loss) on derivative
Realized and Unrealized Gain (Loss) on Hedge	37.5	132.2	2.7
Realized and Unrealized Gain (Loss) on Hedged Item	(70.7)	(150.9)	3.1
Derivatives not designated as hedging instruments
Gain (loss) on derivative
Realized and Unrealized Gain (Loss)	46.3	83.6	16.0
Derivatives not designated as hedging instruments \| Commodity contracts \| Revenue
Gain (loss) on derivative
Realized and Unrealized Gain (Loss)	171.7	64.5	25.4
Derivatives not designated as hedging instruments \| Commodity contracts \| Cost of revenue.
Gain (loss) on derivative
Realized and Unrealized Gain (Loss)	(139.0)	2.2	(5.4)
Derivatives not designated as hedging instruments \| Foreign currency contracts \| Revenue
Gain (loss) on derivative
Realized and Unrealized Gain (Loss)	4.1	4.3
Derivatives not designated as hedging instruments \| Foreign currency contracts \| Other income (expense), net
Gain (loss) on derivative
Realized and Unrealized Gain (Loss)	$ 9.5	$ 12.6	$ (4.0)