Stock-based Compensation (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Stock Options [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Contractual term	10 years
Years until vest	3 years
Stock options, subject to performance or market-based vesting conditions	0
Unrecognized compensation expense	$ 31
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 9 months 18 days
Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Years until vest	4 years
Unrecognized compensation expense	131
Expected weighted average period (in years) of nonvested stock options to be recognized	2 years 2 months 12 days
Performance Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Requisite service period	37 months
Contractual terms of award	We expense the fair value of the units that are probable of being earned based on our forecasted ROIC over the 3-year performance period.
ROIC performance period	3 years
Unrecognized compensation expense	$ 66
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 8 months 12 days