Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Contract Acquisition Costs
Revenue other than customer contracts (as a percent)	1.00%	1.00%
Deferred contract costs	$ 153	$ 145
Long-term revenue contracts (as a percent)	25.00%
Weighted average remaining contract term	5 years
Deferred Sales Incentives [Member]
Contract Acquisition Costs
Deferred contract costs	$ 117	109
Selling, General and Administrative Expenses [Member]
Contract Acquisition Costs
Deferred contract costs amortization	23	22
Reduction to Sales [Member]
Contract Acquisition Costs
Deferred contract costs amortization	$ 17	$ 35
Minimum [Member]
Contract Acquisition Costs
Deferred revenue recognition period	1 month
Contract amortization period	5 years
Maximum [Member]
Contract Acquisition Costs
Deferred revenue recognition period	3 months
Contract amortization period	13 years