CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) (USD $) In Millions, unless otherwise specified	Total	Common Stock	Premium on Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest	Treasury Stock
Balance at Dec. 31, 2012	$ 3,072.4	$ 1.0	$ 1,046.4	$ 1,772.4	$ (49.1)	$ 305.2	$ (3.5)
Changes in Stockholders' Equity
Net income	336.2	0	0	330.0	0	6.2	0
Other comprehensive income, net of tax	3.4	0	0	0	3.3	0.1	0
Dividends declared on common stock	(124.2)	0	0	(124.2)	0	0	0
Issuance of common stock	10.8	0	10.8	0	0	0	0
Stock-based compensation and other	(1.5)	0	(4.2)	0	0	(0.8)	3.5
Contributions from noncontrolling interest partners	107.0	0	22.5	0	0	84.5	0
Distributions to noncontrolling interest partners	(2.5)	0	0	0	0	(2.5)	0
Deconsolidation of Enogex Holdings	(398.3)	0	0	0.5	(6.1)	(392.7)	0
Deferred income taxes attributable to contributions from noncontrolling interest partners	(8.7)	0	(8.7)	0	0	0	0
2-for-1 forward stock split	0	1.0	(1.0)	0	0	0	0
Balance at Sep. 30, 2013	2,994.6	2.0	1,065.8	1,978.7	(51.9)	0	0
Balance at Dec. 31, 2013	3,037.1	2.0	1,071.6	1,991.7	(28.2)	0	0
Changes in Stockholders' Equity
Net income	337.4	0	0	337.4	0	0	0
Other comprehensive income, net of tax	0.9	0	0	0	0.9	0	0
Dividends declared on common stock	(139.5)	0	0	(139.5)	0	0	0
Issuance of common stock	10.1	0	10.1	0	0	0	0
Stock-based compensation and other	(3.0)	0	(3.0)	0	0	0	0
Contributions from noncontrolling interest partners	0
Distributions to noncontrolling interest partners	0
Balance at Sep. 30, 2014	$ 3,243.0	$ 2.0	$ 1,078.7	$ 2,189.6	$ (27.3)	$ 0	$ 0