Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
ASU 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Amortization period of deferred sales commission	4 years
ASU 2014-09 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Sales Commission	$ 200	$ 200
ASU 2014-09 [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred Sales Commission	150	150
ASU 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Leases, Future Minimum Payments Due			$ 450
ASU 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Collections on Beneficial Interests Received in sales of Accounts Receivable and Finance Receivables			270	$ 305
ASU 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted Cash and Cash Equivalents	138	138	$ 179
ASU 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 1	$ 3