Allowance for Losses on Financial Assets Allowance for Losses on Financial Assets (Allowance Disclosure) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Jan. 01, 2020
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	$ (808)	$ (740)	$ (802)	$ (337)
Credit Loss Expense, Reversal	(22)	(406)
Allowance for Credit Loss, Writeoff	16	3
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts Receivable, Allowance for Credit Loss	(413)	(381)	(444)	(138)
Accounts Receivable, Credit Loss Expense (Reversal)	16	(246)
Accounts Receivable, Allowance for Credit Loss, Writeoff	15	3
Contract with Customer, Asset, Allowance for Credit Loss [Roll Forward]
Contract with Customer, Asset, Allowance for Credit Loss	(129)	(188)	(129)	(81)
Contract with Customer, Asset, Credit Loss Expense (Reversal)		(107)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	(16)	(14)	(17)	(5)
Financing Receivable, Credit Loss, Expense (Reversal)	1	(9)
Other Current Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(74)	(48)	(72)	(38)
Credit Loss Expense, Reversal	(3)	(10)
Allowance for Credit Loss, Writeoff	1
Other Noncurrent Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(176)	(109)	$ (140)	$ (75)
Credit Loss Expense, Reversal	$ (36)	$ (34)