Disclosures About Derivative Instruments and Hedging Activities (Details 1) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	$ 19.3	$ 14.1
Total Derivatives Liability	(76.3)	(136.5)
Designated as Hedging Instrument [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	15.0	7.5
Total Derivatives Liability	(70.6)	(118.6)
Derivative Financial Instruments and Other Assets [Member] | Designated as Hedging Instrument [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	9.3	4.4
Derivative Financial Instruments and Other Assets [Member] | Designated as Hedging Instrument [Member] | Foreign Currency Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	1.5	3.1
Derivative Financial Instruments and Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Liability	(9.6)	(65.4)
Derivative Financial Instruments and Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member] | Foreign Currency Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Liability	(0.5)
Derivative Financial Instruments and Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Liability	(60.5)	(53.2)
Derivative Financial Instruments and Other Noncurrent Liabilities [Member] | Derivatives Subject to Utility Rate Regulation [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Liability	(5.5)	(17.9)
Derivative Financial Instruments [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	4.2
Derivative Financial Instruments [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	0.2	6.6
Derivative Financial Instruments [Member] | Derivatives Subject to Utility Rate Regulation [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Assets	4.1
Derivative Financial Instruments, Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Commodity Contracts [Member]
Balance sheet location and fair value of derivative assets and liabilities
Total Derivatives Liability	$ (0.2)	$ 0