Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Valuation account for accounts receivable:
Valuation Account
Balance at Beginning of Period	$ 3	$ 3	$ 3
Charged to Costs and Expenses	0	1	1
Charged to Other Accounts	0	0	0
Deductions	1	1	1
Balance at End of Period	2	3	3
Valuation account for deferred tax assets:
Valuation Account
Balance at Beginning of Period	56	134	47
Charged to Costs and Expenses	6	0	91
Charged to Other Accounts	375	0	0
Deductions	16	78	4
Balance at End of Period	$ 421	$ 56	$ 134