Fair Value Measurements (Fair Value Hierarchy) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	$ 881
Available-for-sale securities		$ 53
Derivative Assets	241	46
Derivative Liability	(98)	(282)
Level 1 | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	773
Available-for-sale securities		53
Derivative Assets	0	0
Derivative Liability	0	0
Level 2 | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	108
Available-for-sale securities		0
Derivative Assets	241	46
Derivative Liability	(98)	(282)
Level 3 | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	0
Available-for-sale securities		0
Derivative Assets	0	0
Derivative Liability	$ 0	$ 0