Stock based compensation (Tables)

12 Months Ended

Dec. 31, 2016

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

Schedule of Share-based Compensation, Stock Options, Activity

The following tables provide additional information related to the options:



2016 Activity	Number of shares (in thousands)		Weighted average exercise price		Remaining weighted average contractual life in years	Intrinsic value (in millions)
Beginning balance	5,250.4		$	12.94	5.7	$	15.1
Granted	818.6		$	9.39		—
Exercised	(151.3	)	$	11.31		—
Forfeited/expired	(46.6	)	$	20.93		—
Total outstanding	5,871.1		$	12.42	5.3	$	59.1
Options exercisable	4,403.4		$	11.74	4.2	$	45.2

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

The assumptions used in the Black-Scholes pricing model to estimate the fair value of the options granted in 2016, 2015 and 2014 are as follows:



	2016	2015	2014
Weighted average fair value	$3.85	$6.36	$8.47
Assumptions
Expected life (in years)	6.25	6.30	6.25
Volatility	40%	33%	27%
Dividend yield	—%	—%	—%
Risk free interest rate	1.40%	1.81%	1.96%

Nonvested Restricted Stock Shares Activity

Further information about the restricted stock units follows (shares in thousands):



Restricted stock units
2016 Activity
Nonvested at beginning of year	1,212.2
Granted	1,075.8
Vested	(363.8	)
Forfeited	(159.1	)
Nonvested at the end of year	1,765.1

Restricted stock generally vests over a three or four year period from the date of grant. Further information about the restricted stock follows (shares in thousands):




2016 Activity
Nonvested at beginning of year	204.2
Granted	397.2
Vested	(174.1	)
Forfeited	(9.5	)
Nonvested at the end of year	417.8