Summary of Significant Accounting Policies (Details 3) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property and Equipment
Property and equipment, gross		$ 7,334	$ 7,105
Less accumulated depreciation		(4,769)	(4,620)
Property and equipment, net		2,565	2,485
Depreciation expense		417	383	$ 388
Goodwill and Intangible Assets
Impairment charges	$ 37	0	37	$ 0
Land
Property and Equipment
Property and equipment, gross		46	48
Building
Property and Equipment
Property and equipment, gross		$ 1,284	1,228
Building | Minimum
Property and Equipment
Estimated useful lives		10 years
Building | Maximum
Property and Equipment
Estimated useful lives		50 years
Equipment
Property and Equipment
Property and equipment, gross		$ 5,656	5,324
Equipment | Minimum
Property and Equipment
Estimated useful lives		5 years
Amortization Period		3 years
Equipment | Maximum
Property and Equipment
Estimated useful lives		20 years
Amortization Period		10 years
Construction In Progress
Property and Equipment
Property and equipment, gross		$ 348	505
Recent Accounting Pronouncements
Recent Accounting Pronouncements
Debt issuance costs classified as a reduction to long-term debt and lease obligations (current and non-current)		$ 117
Prepaid expenses and other current assets | Recent Accounting Pronouncements
Recent Accounting Pronouncements
Net deferred financing costs reclassified to a reduction in the carrying amount of its long-term debt			7
Other assets | Recent Accounting Pronouncements
Recent Accounting Pronouncements
Net deferred financing costs reclassified to a reduction in the carrying amount of its long-term debt			$ 27