Accounting Policies and Supplemental Disclosures - Unearned Revenue (Details) - USD ($) $ in Billions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Unearned revenue		$ 11.6
Unearned revenue, revenue recognized	$ 8.4
Unearned revenue, long-term	2.0	$ 1.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Accounting Policies [Abstract]
Remaining performance obligation, contracts exceeding one year	$ 66.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, weighted average remaining life	3 years 8 months 12 days