Credit Losses on Financial Instruments (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	$ 191
Provision for expected losses	80
Write-offs charged against the allowance	(152)
Recoveries collected	22
Reclassified as held for sale	(24)
Ending balance at September 30, 2021	117
Business
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	109
Provision for expected losses	36
Write-offs charged against the allowance	(58)
Recoveries collected	11
Reclassified as held for sale	(8)
Ending balance at September 30, 2021	90
Mass Markets
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance at January 1, 2020	82
Provision for expected losses	44
Write-offs charged against the allowance	(94)
Recoveries collected	11
Reclassified as held for sale	(16)
Ending balance at September 30, 2021	27
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