Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2016

A summary of the status of our options as of Dec. 31, 2016, and changes during the year, is presented below:



Stock option activity	Shares subject to option		Weighted-average exercise price		Weighted-average remaining contractual term (in years)
Balance at Dec. 31, 2015	35,735,264		$	33.57	3.4
Granted	—		—
Exercised	(12,746,946	)	34.17
Canceled/Expired	(1,746,750	)	41.38
Balance at Dec. 31, 2016	21,241,568		$	32.57	2.8
Vested and expected to vest at Dec. 31, 2016	21,241,568		32.57		2.8
Exercisable at Dec. 31, 2016	21,241,568		32.57		2.8



Stock options outstanding at Dec. 31, 2016
	Options outstanding					Options exercisable (a)
Range of exercise prices	Outstanding	Weighted-average remaining contractual life (in years)	Weighted-average exercise price			Exercisable	Weighted-average exercise price
$ 18 to 31	13,318,863	3.9		$	25.91	13,318,863		$	25.91
$ 31 to 41	1,587,665	0.3		40.29		1,587,665		40.29
$ 41 to 51	6,335,040	1.0		44.63		6,335,040		44.63
$ 18 to 51	21,241,568	2.8		$	32.57	21,241,568		$	32.57


(a)	At Dec. 31, 2015 and 2014, 33,703,283 and 42,137,574 options were exercisable at an average price per common share of $34.27 and $34.38, respectively.



Aggregate intrinsic value of options
(in millions)	2016		2015		2014
Outstanding at Dec. 31,	$	315	$	306	$	409
Exercisable at Dec. 31,	$	315	$	267	$	307

The following table summarizes our nonvested PSU, restricted stock and RSU activity for 2016.



Nonvested PSU, restricted stock and RSU activity	Number of shares		Weighted- average fair value
Nonvested PSUs, restricted stock and RSUs at Dec. 31, 2015	16,983,971		$	34.07
Granted	8,331,206		35.10
Vested	(6,808,038	)	32.10
Forfeited	(511,624	)	34.63
Nonvested PSUs, restricted stock and RSUs at Dec. 31, 2016	17,995,515		$	35.98