Commitments And Contingent Liabilities (Minimum Fuel Purchase Requirements) (Detail) (Power [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Long-term Purchase Commitment [Line Items]
Coverage percentage of nuclear fuel commitments of uranium, enrichment, and fabrication requirements	100.00%
Commitments Through 2018 [Member] | Nuclear Fuel Uranium [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	$ 432
Commitments Through 2018 [Member] | Nuclear Fuel Enrichment [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	428
Commitments Through 2018 [Member] | Nuclear Fuel Fabrication [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	185
Commitments Through 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	1,060
Commitments Through 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	$ 277