Accounting Principles and Practices - Schedule of Changes to Balance Sheet for New Accounting Standards (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Operating lease right-of-use assets	$ 993
Other non-current assets	509		$ 448
Liabilities
Other current liabilities	1,220		936
Non-current operating lease liabilities	978
Other non-current liabilities	$ 973		1,097
Accounting Standards Update 2016-02
Assets
Operating lease right-of-use assets		$ 1,100
Operating lease right-of-use assets
Assets
Operating lease right-of-use assets		1,021
Operating lease right-of-use assets | Accounting Standards Update 2016-02
Assets
Operating lease right-of-use assets		1,021
Other non-current assets
Assets
Other non-current assets		526	448
Other non-current assets | Accounting Standards Update 2016-02
Assets
Other non-current assets		78
Other current liabilities
Liabilities
Other current liabilities		1,155	936
Other current liabilities | Accounting Standards Update 2016-02
Liabilities
Other current liabilities		219
Non-current operating lease liabilities
Liabilities
Non-current operating lease liabilities		1,014
Non-current operating lease liabilities | Accounting Standards Update 2016-02
Liabilities
Non-current operating lease liabilities		1,014
Other non-current liabilities
Liabilities
Other non-current liabilities		963	$ 1,097
Other non-current liabilities | Accounting Standards Update 2016-02
Liabilities
Other non-current liabilities		$ (134)