Segment and Related Information - Electric Utilities' Revenues (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financial data for Products and Services
Electric Utilities Revenues	$ 3,927,000	$ 5,017,000	$ 4,246,000	$ 3,897,000	$ 3,703,000	$ 5,049,000	$ 4,181,000	$ 3,604,000	$ 17,087,000	$ 16,537,000	$ 17,657,000
Electric Utilities [Member]
Financial data for Products and Services
Electric Utilities Revenues									17,035,000	16,478,000	17,587,000
Other Electric Revenue [Member]
Financial data for Products and Services
Electric Utilities Revenues									639,000	616,000	611,000
Wholesale [Member]
Financial data for Products and Services
Electric Utilities Revenues									1,855,000	1,675,000	1,905,000
Retail [Member]
Financial data for Products and Services
Electric Utilities Revenues									$ 14,541,000	$ 14,187,000	$ 15,071,000