Allowance for Losses on Financial Assets Allowance for Losses on Financial Assets (Allowance Disclosure) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	$ (711)	$ (337)
Credit Loss Expense, Reversal	(377)
Allowance for Credit Loss, Writeoff	3
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts Receivable, Allowance for Credit Loss	(431)	(138)
Accounts Receivable, Credit Loss Expense (Reversal)	(296)
Accounts Receivable, Allowance for Credit Loss, Writeoff	3
Contract with Customer, Asset, Allowance for Credit Loss [Roll Forward]
Contract with Customer, Asset, Allowance for Credit Loss	(127)	(81)
Contract with Customer, Asset, Credit Loss Expense (Reversal)	(46)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	(17)	(5)	$ (8)
Financing Receivable, Credit Loss, Expense (Reversal)	(12)
Other Current Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(58)	(38)
Credit Loss Expense, Reversal	(20)
Other Noncurrent Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(78)	$ (75)
Credit Loss Expense, Reversal	$ (3)