Stock-Based Compensation - Stock option activity (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Options
Outstanding at beginning of period, Options	129		129		84
Granted, Options	1		4		45
Exercised, Options	0		(3)	[1]	0
Cancelled, Options	0		0		0
Forfeited, Options	0		(1)		0
Outstanding at end of period, Options	130	[2]	129		129
Weighted Average Exercise Price
Outstanding at beginning of period, Weighted Average Exercise Price	$ 218.38		$ 216.62		$ 193.91
Granted, Weighted Average Exercise Price	$ 229.84		$ 258.37		$ 258.37
Exercised, Weighted Average Exercise Price	$ 0.00		$ 193.13	[1]	$ 0.00
Cancelled, Weighted Average Exercise Price	$ 0.00		$ 0.00		$ 0.00
Forfeited, Weighted Average Exercise Price	$ 0.00		$ 258.37		$ 0.00
Outstanding at end of period, Weighted Average Exercise Price	$ 218.46	[2]	$ 218.38		$ 216.62
Stock option activity, additional disclosure
Options exercisable at end of period, Options	88	[3]	82		80
Options exercisable at end of period, Weighted Average Exercise Price	$ 199.50	[3]	$ 196.33		$ 193.29
Available for grant at end of period	10		11		15
Options exercised, intrinsic value			$ 0.2
Stock options outstanding, intrinsic value	1.9
Stock options outstanding, weighted average remaining contractual term	4 years 5 months
Stock options exercisable, intrinsic value	$ 1.9
Exercisable stock options, weighted average remaining contractual term	2 years 11 months 21 days

[1] The total intrinsic value of the options exercised during the year ended December 31, 2013 was $0.2 million.

[2] Stock options outstanding at December 31, 2014 have a weighted average remaining contractual term of 4.4 years and an aggregate intrinsic value of $1.9 million.

[3] Exercisable stock options at December 31, 2014 have a weighted average remaining contractual term of 3.0 years and an aggregate intrinsic value of $1.9 million.