Commitments And Contingencies (Third-Party Power Purchases) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2014
Long-term Purchase Commitment [Line Items]
Total	$ 1,700
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Long-term agreements range, years	25

Amount of the recorded obligation to transfer funds in the future for fixed or minimum amounts or quantities of goods or services at fixed or minimum prices (for example, as in take-or-pay contracts or throughput contracts).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 440

-SubTopic 10

-Section 50

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6394976&loc=d3e25383-109308

Name:	us-gaap_RecordedUnconditionalPurchaseObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant