Debt and Capital Lease Obligations (Debt) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Notional Amount of Interest Rate Derivatives	$ 200.0
Derivative, Cap Interest Rate	1.50%
Senior Notes	550.0		550.0
Senior Notes, Current	0		0
Senior Notes, Noncurrent	550.0		550.0
Loans Payable	196.6		196.1
Loans Payable, Current	0		0
Loans Payable, Noncurrent	196.6		196.1
Notes Payable	29.2		16.0
Notes Payable, Current	19.7		3.4
Notes Payable, Noncurrent	9.5		12.6
Debt and Capital Lease Obligations	775.8		762.1
Current portion of long-term debt and short term borrowings	19.7		3.4
Long-term debt and capital lease obligations, less current portion	756.1		758.7
Short Term Solar Energy System Financing And Current Portion Of Long Term Solar Energy System Financing And Capital Lease Obligations	261.6		97.8
Long-term solar energy system financing and capital lease obligations, less current portion, including consolidated variable interest entities	2,080.9		1,508.4
Debt And Capital Lease Obligations Including Solar Energy Systems Financing	3,118.3		2,368.3
Debt And Capital Lease Obligations Including Solar Energy Systems Financing, Current	281.3		101.2
Long Term Debt And Capital Lease Obligations Including Solar Energy Systems Financing	2,837.0		2,267.1
Solar Energy [Member]
Debt Instrument [Line Items]
Short-term Debt	56.5
Short-term Debt, Weighted Average Interest Rate		8.00%	6.50%
Capital Lease Obligations, Current	7.1		7.5
Capital Lease Obligations, Noncurrent	129.7		85.8
Sale Leaseback Transaction, Amount Due under Financing Arrangement	1,169.6		1,107.2
Financing Obligations, Current	12.9		14.3
Long-term Finance Obligations	1,156.7		1,092.9
Other System Financing transactions	120.8		119.7
Other system financing transactions, current	0		0
Other system financing transactions, noncurrent	120.8		119.7
Long Term Solar Energy Systems Financing And Capital Leases	2,342.5		1,606.2
Short Term Solar Energy System Financing And Current Portion Of Long Term Solar Energy System Financing And Capital Lease Obligations	261.6		97.8
Long-term solar energy system financing and capital lease obligations, less current portion, including consolidated variable interest entities	2,080.9		1,508.4
Construction and Term Debt [Member] | Solar Energy [Member]
Debt Instrument [Line Items]
Short-term Debt	0		0
Long-term Debt	858.8		271.3
Long-term Debt, Current Maturities	185.1		61.3
Long-term Debt, Excluding Current Maturities	673.7		210.0
SunEdison [Member] | Solar Energy [Member]
Debt Instrument [Line Items]
Capital Lease Obligations	136.8		93.3
Construction and Term Debt [Member] | Solar Energy [Member]
Debt Instrument [Line Items]
Short-term Debt	$ 56.5		$ 14.7
Debt Instrument, Redemption, Period Three [Member] | Second Lien Credit Agreement [Member]
Debt Instrument [Line Items]
Debt Instrument, Call Premium, Percentage		2.00%