Commitments and Other Contingencies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Total rent expense incurred under operating leases	$ 426	$ 536	$ 581
Loss Contingencies [Line Items]
Recorded Unconditional Purchase Obligation	124
Other Current Liabilities [Member]
Loss Contingencies [Line Items]
Recorded Unconditional Purchase Obligation	47
Other Current Liabilities [Member] | Fair Value Guarantee [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual	68
Other Noncurrent Liabilities [Member]
Loss Contingencies [Line Items]
Recorded Unconditional Purchase Obligation	77
Other Noncurrent Liabilities [Member] | Fair Value Guarantee [Member]
Loss Contingencies [Line Items]
Loss Contingency Accrual	$ 28