Stock based compensation (Tables)

12 Months Ended

Dec. 31, 2013

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 (share data in millions):



2013 Activity	Number of shares		Weighted average exercise price		Remaining weighted average contractual life in years	Intrinsic value
Beginning balance	7.1		$	9.84	7.4	$	105.6
Granted	0.3		$	26.05
Exercised	(0.9	)	$	7.48
Forfeited/expired	(0.5	)	$	14.7
Total outstanding	6.0		$	10.76	6.8	$	22.8
Options exercisable	3.8		$	8.58	6.3	$	11.5

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 2013, 2012 and 2011 are as follows:



	2013	2012	2011
Weighted average fair value	$8.41	$6.81	$5.08
Assumptions
Expected life (in years)	6.25	6.25	6.25
Volatility	30%	36%	34%
Dividend yield	—%	—%	—%
Risk free interest rate	1.17%	1.13% - 1.22%	1.19% - 2.64%

Nonvested Restricted Stock Shares Activity

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



Restricted stock units
2013 Activity
Nonvested at beginning of year	16.8
Granted	450.3
Vested	(16.8	)
Forfeited	(45.9	)
Nonvested at the end of year	404.4

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



Restricted stock
2013 Activity
Nonvested at beginning of year	1,255.6
Granted	95.4
Vested	(464.2	)
Forfeited	(64.5	)
Nonvested at the end of year	822.3