Commitments And Contingencies (Legal And Regulatory Contingencies) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Loss Contingencies [Line Items]
Number of self-reports filed with the CPUC	48
Potential Equity Issuances To Fund Penalites	$ 2,250
Utility Forecast On Penalties	477
San Bruno Explosion [Member]
Loss Contingencies [Line Items]
Estimated maximum amount for third party claims for San Bruno	600
San Bruno Explosion [Member] | San Mateo County Superior Court [Member]
Loss Contingencies [Line Items]
Number of plaintiffs	480
Number Plaintiffs Settled	140
Tort Lawsuits [Member] | San Bruno Explosion [Member] | San Mateo County Superior Court [Member]
Loss Contingencies [Line Items]
Number of lawsuits	160
Class Action Lawsuits [Member] | San Bruno Explosion [Member] | San Mateo County Superior Court [Member]
Loss Contingencies [Line Items]
Number of lawsuits	2
PGE Corporation And Utility [Member]
Loss Contingencies [Line Items]
Accrued legal liabilities	38	34
Probable penalty amount	200	200
Pacific Gas And Electric Company [Member]
Loss Contingencies [Line Items]
Accrued legal liabilities	73	146	277	214
Capital Expenditures Recovery Allowed	1,000
Capital Expenditure Recovery Requested	1,400
Disallowed capital expenditures	353
Utility liability insurance for damages	992
Utility liability insurance deductible	10
Cumulative insurance recoveries for cost incurred related to third-party claims	284
Pacific Gas And Electric Company [Member] | San Bruno Explosion [Member]
Loss Contingencies [Line Items]
Cumulative charge	455
Cumulative payments	382
Estimated possible additional loss contingency liability	$ 145