Fair Value (Nonrecurring Unobservable Inputs) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 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 [Member] | 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 [Member] | 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 [Member] | 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%
Fair Value [Member] | Market Approach [Member] | Weighted Average [Member] | Long Lived Assets Held For Sale [Member] | Wind turbines [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value, Nonrecurring	$ 0	[1]
Fair Value [Member] | Level 3 [Member] | Long Lived Assets Held And Used [Member] | Beaver Valley [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value, Nonrecurring	$ 15	[1]

[1] See Note 13 — Asset Impairment Expense for further information.