Debt and Credit Agreements (Credit Facilities and Letters of Credit) (Details) (Letter of Credit, USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Jun. 30, 2013 Walnut Creek Project	Apr. 30, 2013 Other EME Subsidiaries
Line of Credit Facility [Line Items]
Standby letters of credit	$ 244	$ 30
Standby letters of credit expiring in 2013	51
Standby letters of credit expiring in 2014	123
Standby letters of credit expiring in 2017	20
Standby letters of credit expiring in 2018	19
Standby letters of credit expiring in 2021	18
Standby letters of credit expiring in 2022	13
Cash collateral	45
Credit facility, maximum borrowing capacity			$ 75