Other Income (Expense) - net (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Other Income [Line Items]
Other income	$ 13	$ 21
Other Expense [Line Items]
Other expense	30	26
Other Income (Expense) - net	(17)	(5)
Economic Foreign Currency Exchange Contracts [Member]
Other Expense [Line Items]
Other expense	18	2
Charitable Contributions [Member]
Other Expense [Line Items]
Other expense	4	3
WPD Midlands Acquisition Related Costs [Member]
Other Expense [Line Items]
Other expense	0	11
Net Hedge Losses Associated With 2011 Bridge Facility [Member]
Other Expense [Line Items]
Other expense	0	7
Miscellaneous Domestic Other Expense [Member]
Other Expense [Line Items]
Other expense	6	2
Miscellaneous UK Other Expense [Member]
Other Expense [Line Items]
Other expense	2	1
Earnings On Securities In Nuclear Decommissioning Trust Funds [Member]
Other Income [Line Items]
Other income	8	15
Interest Income [Member]
Other Income [Line Items]
Other income	1	2
Allowance For Funds Used During Construction [Member]
Other Income [Line Items]
Other income	2	1
Miscellaneous Domestic Other Income [Member]
Other Income [Line Items]
Other income	$ 2	$ 3