Commitments And Contingent Liabilities (Minimum Fuel Purchase Requirements) (Detail) - Power [Member] $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Long-term Purchase Commitment [Line Items]
Coverage percentage of nuclear fuel commitments of uranium, enrichment, and fabrication requirements	100.00%
Commitments Through 2017 [Member] | Nuclear Fuel Uranium [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	$ 301
Commitments Through 2017 [Member] | Nuclear Fuel Enrichment [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	356
Commitments Through 2017 [Member] | Nuclear Fuel Fabrication [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	192
Commitments Through 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	1,029
Commitments Through 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Total minimum purchase requirements	$ 215