Stock-Based Compensation - Net Change in Amounts Capitalized or Accrued (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Other assets	$ (345)	$ (269)	$ (174)
Deferred Compensation, Share-based Payments
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accrued expenses (accrued warranty expenses)	0	(1)
Other assets	$ (19)	$ 2