Fair Value (Nonrecurring Unobservable Inputs) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Discounted Cash Flow [Member] | Long Lived Assets Held And Used [Member] | Beaver Valley [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Weighted Average Cost Of Capital Input	7.00%
Discounted Cash Flow [Member] | Minimum | Long Lived Assets Held And Used [Member] | Beaver Valley [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Annual Revenue Growth Input	3.00%
Pretax Operating Margin Input	(42.00%)
Discounted Cash Flow [Member] | Maximum | Long Lived Assets Held And Used [Member] | Beaver Valley [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Annual Revenue Growth Input	45.00%
Pretax Operating Margin Input	41.00%
Discounted Cash Flow [Member] | Weighted Average | Long Lived Assets Held And Used [Member] | Beaver Valley [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Annual Revenue Growth Input	19.00%
Pretax Operating Margin Input	25.00%
Market Approach [Member] | Minimum | Long Lived Assets Held For Sale [Member] | Wind Turbines [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Indicative offer prices	12
Market Approach [Member] | Maximum | Long Lived Assets Held For Sale [Member] | Wind Turbines [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Indicative offer prices	38
Market Approach [Member] | Weighted Average | Long Lived Assets Held For Sale [Member] | Wind Turbines [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Indicative offer prices	25