Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of computation of basic and diluted earnings per share

Computation of Earnings Per Share

	Year Ended December 31,
	2017		2016		2015
	(in millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to AGL	$	730	$	881	1,056
Less: Distributed and undistributed income (loss) available to nonvested shareholders	1		1		1
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, basic	$	729	$	880	1,055
Basic shares	120.6		133.0		148.1
Basic EPS	$	6.05	$	6.61	$	7.12
Diluted EPS:
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, basic	$	729	$	880	$	1,055
Plus: Re-allocation of undistributed income (loss) available to nonvested shareholders of AGL and subsidiaries	0		0		0
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, diluted	$	729	$	880	$	1,055
Basic shares	120.6		133.0		148.1
Dilutive securities:
Options and restricted stock awards	1.7		1.1		0.9
Diluted shares	122.3		134.1		149.0
Diluted EPS	$	5.96	$	6.56	$	7.08
Potentially dilutive securities excluded from computation of EPS because of antidilutive effect	0.1		0.3		0.5

Schedule of antidilutive securities excluded from computation of earnings per share

Computation of Earnings Per Share

	Year Ended December 31,
	2017		2016		2015
	(in millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to AGL	$	730	$	881	1,056
Less: Distributed and undistributed income (loss) available to nonvested shareholders	1		1		1
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, basic	$	729	$	880	1,055
Basic shares	120.6		133.0		148.1
Basic EPS	$	6.05	$	6.61	$	7.12
Diluted EPS:
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, basic	$	729	$	880	$	1,055
Plus: Re-allocation of undistributed income (loss) available to nonvested shareholders of AGL and subsidiaries	0		0		0
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries, diluted	$	729	$	880	$	1,055
Basic shares	120.6		133.0		148.1
Dilutive securities:
Options and restricted stock awards	1.7		1.1		0.9
Diluted shares	122.3		134.1		149.0
Diluted EPS	$	5.96	$	6.56	$	7.08
Potentially dilutive securities excluded from computation of EPS because of antidilutive effect	0.1		0.3		0.5