Credit Losses on Financial Instruments (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	$ 191
Provision for expected losses	53
Write-offs charged against the allowance	(117)
Recoveries collected	25
Ending balance at June 30, 2021	152
Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	109
Provision for expected losses	21
Write-offs charged against the allowance	(35)
Recoveries collected	8
Ending balance at June 30, 2021	103
Mass Markets
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	82
Provision for expected losses	32
Write-offs charged against the allowance	(82)
Recoveries collected	17
Ending balance at June 30, 2021	49
Consumer Reclassed to Mass Markets
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	70
Business Reclassed to Mass Markets
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	$ 12