Financial Instruments - Cash Flow Hedges Effect on Accumulated Other Comprehensive Earnings/(Losses), Net of Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Balance at beginning of period	$ 27,317	$ 25,602	$ 26,025
Transfer of realized (gains)/losses in fair value to earnings	285	279	169
Balance at end of period	27,654	27,317	25,602
Cash Flow Hedges
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Unrealized gain/(loss) in fair value	(109)	(199)	(45)
Derivative Cash Flow Hedges
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Balance at beginning of period	(213)	(168)	(114)
Balance at end of period	(161)	(213)	(168)
Derivative Cash Flow Hedges | Cash Flow Hedges
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net [Abstract]
Balance at beginning of period	(213)	(168)	(114)
Transfer of realized (gains)/losses in fair value to earnings	161	154	(9)
Unrealized gain/(loss) in fair value	(109)	(199)	(45)
Balance at end of period	$ (161)	$ (213)	$ (168)