Common Equity (Tables)

9 Months Ended

Sep. 30, 2011

Common Equity (Tables) [Abstract]

Assumptions for valuing options using binomial option pricing model

	2011		2010
Risk-free interest rate	0.2% - 3.4%		0.2% - 3.9%
Dividend yield	3.9	%	3.7	%
Expected volatility	19.0	%	20.3	%
Expected forfeiture rate	2.0	%	2.0	%
Expected life (years)	5.5		5.9

Stock option activity

					Weighted-
					Average
			Weighted-		Remaining	Aggregate
	Number of		Average		Contractual Life	Intrinsic Value
Stock Options	Options		Exercise Price		(Years)	(Millions)
Outstanding as of July 1, 2011	11,925,226		$	21.40
Granted	—		$	—
Exercised	(272,412	)	$	17.82
Forfeited	—		$	—
Outstanding as of September 30, 2011	11,652,814		$	21.49
Outstanding as of January 1, 2011	13,036,466		$	20.81
Granted	458,180		$	29.35
Exercised	(1,841,832	)	$	18.68
Forfeited	—		$	—
Outstanding as of September 30, 2011	11,652,814		$	21.49	5.5	$	114.3
Exercisable as of September 30, 2011	8,499,304		$	20.97	4.7	$	87.7

Stock options outstanding

	Options Outstanding				Options Exercisable
		Weighted-Average				Weighted-Average
				Remaining				Remaining
	Number of	Exercise		Contractual	Number of	Exercise		Contractual
Range of Exercise Prices	Options	Price		Life (Years)	Options	Price		Life (Years)
$11.33 to $17.10	2,405,276	$	15.99	2.5	2,405,276	$	15.99	2.5
$19.74 to $21.11	3,771,448	$	20.61	6.2	1,569,748	$	19.91	4.6
$23.88 to $29.35	5,476,090	$	24.50	6.3	4,524,280	$	23.98	5.8
	11,652,814	$	21.49	5.5	8,499,304	$	20.97	4.7

Non-vested options

Non-Vested Stock Options	Number of Options		Weighted-Average Fair Value
Non-vested as of July 1, 2011	3,153,510		$	3.78
Granted	—		$	—
Vested	—		$	—
Forfeited	—		$	—
Non-vested as of September 30, 2011	3,153,510		$	3.78
Non-vested as of January 1, 2011	5,272,570		$	4.27
Granted	458,180		$	3.17
Vested	(2,577,240	)	$	4.66
Forfeited	—		$	—
Non-vested as of September 30, 2011	3,153,510		$	3.78

Restricted stock activity

Restricted Shares	Number of Shares		Weighted-Average Grant Date Fair Value
Outstanding as of July 1, 2011	198,820
Granted	—		$	—
Released	—		$	—
Forfeited	—		$	—
Outstanding as of September 30, 2011	198,820
Outstanding as of January 1, 2011	205,404
Granted	74,850		$	29.00
Released	(78,624	)	$	19.03
Forfeited	(2,810	)	$	26.45
Outstanding as of September 30, 2011	198,820

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

	Three Months Ended September 30				Nine Months Ended September 30
	2011		2010		2011		2010
	(Millions of Dollars)
Stock options	$	0.6	$	1.9	$	1.9	$	5.7
Performance units	7.3		10.3		11.7		20.9
Restricted stock	0.4		0.3		1.3		1.1
Share-based compensation expense	$	8.3	$	12.5	$	14.9	$	27.7
Related Tax Benefit	$	3.4	$	5.0	$	6.0	$	11.1