Income Taxes Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Tax Contingency [Line Items]
Effective income tax rate	19.10%	18.90%
Decrease in uncertain tax positions	$ 19
Amount of liability for uncertain tax positions that would impact the effective tax rate if recognized	133
Other Noncurrent Liabilities [Member]
Income Tax Contingency [Line Items]
Liability for uncertain tax positions, noncurrent	186
Liability for uncertain tax positions, interest	25
Liability for uncertain tax positions, penalties	$ 11