Allowance for Losses on Financial Assets Allowance for Losses on Financial Assets (Allowance Disclosure) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	$ (374)	$ (337)
Credit Loss Expense, Reversal	(38)
Allowance for Credit Loss, Writeoff	1
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Accounts Receivable, Allowance for Credit Loss	(166)	(138)
Accounts Receivable, Credit Loss Expense (Reversal)	(29)
Accounts Receivable, Allowance for Credit Loss, Writeoff	1
Contract with Customer, Asset, Allowance for Credit Loss [Roll Forward]
Contract with Customer, Asset, Allowance for Credit Loss	(80)	(81)
Contract with Customer, Asset, Credit Loss Expense (Reversal)	1
Contract with Customer, Asset, Allowance for Credit Loss, Writeoff
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Financing Receivable, Allowance for Credit Loss	(5)	(5)	$ (8)
Financing Receivable, Credit Loss, Expense (Reversal)
Financing Receivable, Allowance for Credit Loss, Writeoff
Other Current Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(48)	(38)
Credit Loss Expense, Reversal	(10)
Allowance for Credit Loss, Writeoff
Other Noncurrent Assets
Allowance for Losses on Financial Assets [Line Items]
Allowance for Credit Loss	(75)	$ (75)
Credit Loss Expense, Reversal
Allowance for Credit Loss, Writeoff