Asset Retirement Obligation By Type (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities	$ 2,832		$ 2,665
Total ARO liability	753		696		490
Fossil fuel facilities [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	334		315
Quad Cities Station [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	265		254
Wind generating facilities [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	75		59
Offshore pipeline facilities [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	31		35
Solar generating facilities [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	9		5
Other [Member]
Asset Retirement Obligations By Type [Line Items]
Total ARO liability	39		28
Cost of removal [Member]
Asset Retirement Obligations By Type [Line Items]
Regulatory Liabilities	2,215	[1]	2,009	[1]
Quad Cities Station nuclear decommissioning trust funds [Member]
Asset Retirement Obligations By Type [Line Items]
Nuclear decommissioning trust funds	$ 424		$ 394

[1] Amounts represent estimated costs, as accrued through depreciation rates and exclusive of ARO liabilities, of removing regulated property, plant and equipment in accordance with accepted regulatory practices. Amounts are deducted from rate base or otherwise accrue a carrying cost.