Earnings Per Share (Tables)

6 Months Ended

Jun. 30, 2012

Earnings Per Share [Abstract]

Schedule of computation of basic and diluted earnings per share

Computation of Earnings Per Share

	Second Quarter					Six Months
	2012		2011			2012			2011
	(in millions, except per share amounts)
Basic earnings per share (“EPS”):
Net income (loss) attributable to AGL	$	376.5	$	(43.1	)	$	(106.5	)	$	96.2
Less: Distributed and undistributed income (loss) available to nonvested shareholders	0.5		—			(0.2		)	0.1
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	$	376.0	$	(43.1	)	$	(106.3	)	$	96.1
Basic shares	186.3		184.2			184.4			184.0
Basic EPS	$	2.02	$	(0.23	)	$	(0.58	)	$	0.52
Diluted EPS:
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	$	376.0	$	(43.1	)	$	(106.3	)	$	96.1
Plus: Re-allocation of undistributed income (loss) available to nonvested shareholders of AGL and subsidiaries	—		—			—			—
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	$	376.0	$	(43.1	)	$	(106.3	)	$	96.1
Basic shares	186.3		184.2			184.4			184.0
Effect of dilutive securities:
Options and restricted stock awards	0.7		—			—			0.9
Equity units	—		—			—			2.5
Diluted shares	187.0		184.2			184.4			187.4
Diluted EPS	$	2.01	$	(0.23	)	$	(0.58	)	$	0.51
Potentially dilutive securities excluded from computation of EPS because of antidilutive effect	13.0		19.5			15.9			2.9