Consolidated Statements of Common Equity (USD $) In Millions	Total	Common Stock [Member]	Other Paid In Capital [Member]	Retained Earnings [Member]
Beginning - Balance at Dec. 31, 2010	$ 3,802.1	$ 2.3	$ 721.5	$ 3,078.3
Net income	526.2			526.2
Common stock cash dividends of $1.04, $1.20, and $1.445 per share for Year ended 2011, 2012 and 2013, respectively	(242.0)			(242.0)
Exercise of stock options	54.4		54.4
Purchase of common stock	(193.9)		(193.9)
Tax benefit from share based compensation	11.9		11.9
Stock-based compensation and other	4.6		4.6
Ending - Balance at Dec. 31, 2011	3,963.3	2.3	598.5	3,362.5
Net income	546.3			546.3
Common stock cash dividends of $1.04, $1.20, and $1.445 per share for Year ended 2011, 2012 and 2013, respectively	(276.3)			(276.3)
Exercise of stock options	49.8		49.8
Purchase of common stock	(153.2)		(153.2)
Stock-based compensation and other	5.2		5.2
Ending - Balance at Dec. 31, 2012	4,135.1	2.3	500.3	3,632.5
Net income	577.4			577.4
Common stock cash dividends of $1.04, $1.20, and $1.445 per share for Year ended 2011, 2012 and 2013, respectively	(328.9)			(328.9)
Exercise of stock options	48.5		48.5
Purchase of common stock	(223.4)		(223.4)
Tax benefit from share based compensation	18.1		18.1
Stock-based compensation and other	6.2		6.2
Ending - Balance at Dec. 31, 2013	$ 4,233.0	$ 2.3	$ 349.7	$ 3,881.0