Statements of Consolidated Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statements of Consolidated Comprehensive Income
Natural gas, tax benefit	$ (5,448)	$ (62,383)	$ (15,595)	$ (65,488)
Interest rate, tax expense (benefit)	25	(1,322)	75	(4,487)
Pension and other post-retirement benefits liability adjustment, tax expense	$ 307	$ 369	$ 920	$ 583