Additional Shareholders' Equity Information - Accumulated Other Comprehensive Loss (AOCL) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	$ 10,484	$ 10,619	$ 9,600
Realized Amounts Reclassified Into Earnings	1	(2)	5
Unrealized Change in Fair Value			(4)
Ending Balance	9,055	10,484	10,619
Interest Rate Cash Flow Hedge
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance		(20)	(21)
Realized Amounts Reclassified Into Earnings		(3)	1
Unrealized Change in Fair Value			0
Ending Balance			(20)
Interest Rate Cash Flow Hedge
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(23)
Realized Amounts Reclassified Into Earnings	1
Ending Balance	(22)	(23)
Other Postretirement Benefit Plans
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(9)	(10)	(10)
Realized Amounts Reclassified Into Earnings	0	1	4
Unrealized Change in Fair Value			(4)
Ending Balance	(9)	(9)	(10)
Total
Accumulated Other Comprehensive Loss (AOCL)
Beginning Balance	(32)	(30)	(31)
Ending Balance	$ (31)	$ (32)	$ (30)

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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