Income Taxes (Deferred Tax Assets and Deferred Tax Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Liabilities:
Differences between book and tax basis of property	$ (1,308)	$ (1,426)
Deferred Tax Liabilities, Investment in US Tax Partnerships	(332)	(44)
Deferred income taxes	1,100	1,213
Other taxable temporary differences	(403)	(287)
Deferred Tax Liabilities, Gross	(2,043)	(1,757)
Deferred Tax Assets:
Operating loss carryforwards	1,156	1,060
Capital loss carryforwards	73	57
Bad debt and other book provisions	87	74
Tax credit carryforwards	78	33
Other deductible temporary differences	471	300
Total gross deferred tax asset	1,865	1,524
Less: Valuation allowance	(634)	(824)
Total net deferred tax asset	1,231	700
Total deferred tax liability	$ (812)	$ (1,057)