Accounting Policies and Supplemental Disclosures - Unearned Revenue (Details) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Unearned revenue		$ 10.2
Unearned revenue, revenue recognized	$ 7.1
Unearned revenue, long-term	1.9	$ 2.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Accounting Policies [Abstract]
Remaining performance obligation, contracts exceeding one year	$ 44.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, weighted average remaining life	3 years 4 months 24 days