Revenue Recognition Revenue Recognition - Allowance for Doubtful Accounts (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018 USD ($)
Allowance for Doubtful Accounts Receivable	$ 51
Provision for Doubtful Accounts	(3)
Allowance for Loan and Lease Losses Write-offs, Net	(8)
Allowance for Doubtful Accounts Receivable	40
Allowance for Credit Loss [Member]
Allowance for Doubtful Accounts Receivable	44
Provision for Doubtful Accounts	0
Allowance for Loan and Lease Losses Write-offs, Net	(7)
Allowance for Doubtful Accounts Receivable	37
Allowance for Trade Receivables [Member]
Allowance for Doubtful Accounts Receivable	7
Provision for Doubtful Accounts	(3)
Allowance for Loan and Lease Losses Write-offs, Net	(1)
Allowance for Doubtful Accounts Receivable	$ 3