Accounting Changes (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating lease commitments		$ 6,400
Deferred tax assets, noncurrent	$ 4,809	4,822
Debt issuance costs	95	74
Accounting Standards Update 2015-03 Interest-Imputation of Interest
Debt issuance costs	$ 95	$ 74
Deferred Tax Assets | Accounting Standards Update 2015-17 - Balance Sheet Classification of Deferred Taxes
Current deferred tax assets			$ 2,000
Other liabilities | Accounting Standards Update 2015-17 - Balance Sheet Classification of Deferred Taxes
Current deferred tax liabilities			19
Deferred tax assets, noncurrent			$ 178