Recently Adopted and Recently Issued Accounting Guidance (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Mar. 30, 2012	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounting Policies [Abstract]
Restricted cash		$ 5	$ 5	$ 5	$ 5	$ 4
Summary Of Significant Accounting Policies [Line Items]
Reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables	$ 50			420	285
Reclassification of cash paid for debt prepayments including extinguishment costs from operating to financing activities				17	52
Adjustment to operating income based on adoption of new accounting guidance		$ 324	320	$ 657	603
ASU 2016-15
Summary Of Significant Accounting Policies [Line Items]
Reclassification of cash paid for debt prepayments including extinguishment costs from operating to financing activities					(52)
Adjustments for New Accounting Pronouncement
Summary Of Significant Accounting Policies [Line Items]
Adjustment to operating income based on adoption of new accounting guidance			$ 39		$ 77