Share-based compensation plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, minimum (in years)	1Y
Award vesting period, maximum (in years)	5Y
Compensation cost	$ 12,100,000	$ 13,700,000	$ 15,200,000
Income tax benefit from compensation cost	4,200,000	1,500,000	5,300,000
Additional disclosures [Abstract]
Closing stock price at end of period (in dollars per share)	$ 3.73
Weighted average exercise price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 60.08
Granted (in dollars per share)	$ 0
Exercised (in dollars per share)	$ 0
Forfeited or expired (in dollars per share)	$ 58.28
Outstanding, end of period (in dollars per share)	$ 60.50	$ 60.08
Shares subject to option [Roll Forward]
Outstanding, beginning of period (in shares)	1,749,700
Granted (in shares)	0
Exercised (in shares)	0
Forfeited or expired (in shares)	(329,200)
Outstanding, end of period (in shares)	1,420,500	1,749,700
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (in shares)		1,420,500
Options outstanding, remaining average life (in years)		1.1
Options outstanding, weighted average exercise price (in dollars per share)		$ 60.50
Options exercisable (in shares)		1,420,500
Options exercisable, remaining average life (in years)		1.1
Options exercisable, weighted average exercise price (in dollars per share)		$ 60.50
$43.70 - $43.70 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit (in dollars per share)		$ 43.70
Exercise price range, upper range limit (in dollars per share)		$ 43.70
Options outstanding (in shares)		349,500
Options outstanding, remaining average life (in years)		1.1
Options outstanding, weighted average exercise price (in dollars per share)		$ 43.70
Options exercisable (in shares)		349,500
Options exercisable, remaining average life (in years)		1.1
Options exercisable, weighted average exercise price (in dollars per share)		$ 43.70
$63.80 - $68.20 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit (in dollars per share)		$ 63.80
Exercise price range, upper range limit (in dollars per share)		$ 68.20
Options outstanding (in shares)		1,071,000
Options outstanding, remaining average life (in years)		1.1
Options outstanding, weighted average exercise price (in dollars per share)		$ 65.98
Options exercisable (in shares)		1,071,000
Options exercisable, remaining average life (in years)		1.1
Options exercisable, weighted average exercise price (in dollars per share)		$ 65.98
Stock Options [Member]
Additional disclosures [Abstract]
Aggregate intrinsic value of options outstanding	0
Aggregate intrinsic value of options exercisable	0
Restricted Stock [Member]
Additional disclosures [Abstract]
Restricted stock, performance shares (in shares)	2,300,000
Restricted stock, time vested shares (in shares)	600,000
Total fair value of restricted stock vested	14,900,000	8,500,000	1,300,000
Weighted average grant date fair market value [Abstract]
Restricted stock outstanding at end of period (in dollars per share)	$ 14.69
Granted (in dollars per share)	$ 8.94	$ 6.82	$ 3.11
Vested (in dollars per share)	$ 8.32
Forfeited (in dollars per share)	$ 60.01
Restricted stock outstanding at end of period (in dollars per share)	$ 12.88	$ 14.69
Shares [Roll Forward]
Restricted stock outstanding at beginning of period (in shares)	3,457,266
Granted (in shares)	1,368,295
Vested (in shares)	(1,698,956)
Forfeited (in shares)	(180,843)
Restricted stock outstanding at end of period (in shares)	2,945,762	3,457,266
2002 Plan [Member]
Additional disclosures [Abstract]
Unrecognized compensation cost	22,600,000
Unrecognized compensation cost, performance shares	21,600,000
Unrecognized compensation cost, time vested shares	1,000,000
Weighted-average period for recognition of compensation cost (in years)	0.2
2002 Plan [Member] | Restricted Stock Units (RSUs) [Member]
Additional disclosures [Abstract]
Unrecognized compensation cost	$ 1,000,000
Weighted-average period for recognition of compensation cost (in years)	2.1
Weighted average grant date fair market value [Abstract]
Granted (in dollars per share)	$ 8.94
Shares [Roll Forward]
Granted (in shares)	449,350
Forfeited (in shares)	5,400
2011 Plan [Member]
Additional disclosures [Abstract]
Shares available for future grants (in shares)	7,000,000