Income Taxes Components of Net Deferred Income Tax Liability (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred income tax assets: [Abstract]
Federal and state carryforwards	$ 781	$ 1,001
Regulatory liabilities	812	825
AROs	249	234
Employee benefits	187	75
Derivative contracts	62	28
Other	781	740
Total deferred income tax assets	2,872	2,903
Valuation allowances	(23)	(29)
Total deferred income tax assets, net	2,849	2,874
Deferred income tax liabilities: [ Abstract]
Property-related items	(11,989)	(10,727)
Regulatory assets	(1,374)	(1,047)
Investments	(699)	(767)
Other	(301)	(287)
Total deferred income tax liabilities	(14,363)	(12,828)
Net deferred income tax liability	(11,514)	(9,954)
Reflected as: [Abstract]
Current assets - other	291	211
Current liabilities - other	(3)	(7)
Deferred income taxes	$ (11,802)	$ (10,158)