Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) (USD $) In Millions, 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
Operating revenues	$ 832.6	$ 866.6	$ 718.0	$ 859.6	$ 750.9	$ 887.6	$ 690.3	$ 765.7	$ 3,276.8	$ 3,094.5	$ 3,221.4
Operating expenses									2,742.9	2,574.8	2,708.1
Operating income	108.6	201.4	103.2	120.7	101.6	213.7	108.8	95.6	533.9	519.7	513.3
Interest expense and other:
Equity earnings from consolidated subsidiaries									(43.7)	(41.3)	(39.3)
Interest expense									172.8	156.7	158.3
Total interest expense and other									97.9	89.5	102.7
Income from continuing operations before income taxes									436.0	430.2	410.6
Income tax benefit									(53.9)	(89.4)	(69.2)
Net income									376.2	335.7	321.9
Parent Company [Member]
Operating revenues									2.0	2.0	4.0
Operating expenses									1.0	1.0	1.0
Operating income									1.0	1.0	3.0
Interest expense and other:
Equity earnings from consolidated subsidiaries									(362.0)	(322.0)	(304.0)
Interest expense									11.0	11.0	11.0
Interest income									(2)	(4)	(2)
Total interest expense and other									(353.0)	(315.0)	(295.0)
Income from continuing operations before income taxes									354.0	316.0	298.0
Income tax benefit									(4.0)	(4.0)	(5.0)
Net income									$ 358.0	$ 320.0	$ 303.0