Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency [Line Items]
Federal rate	21.00%	21.00%	21.00%
Expected income refunds	$ 13
Tax impact related to goodwill impairment		$ 524	$ 72
Income taxes paid	8	4	$ 4
Valuation allowance	783	$ 605
Gross tax liability for tax positions that may not be sustained under a more likely than not threshold	16
Effect of expiration of statute of limitations during next twelve months	$ 2
Deferred income tax payment period	2 years
Deferred income tax payment	$ 60
Percentage of limitation on use	80.00%
Shareholder's Right Plan [Member]
Income Tax Contingency [Line Items]
Beneficial ownership	4.90%
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 1,800
Tax credit expiration year	2036
Research and development credits	$ 12
Internal Revenue Service (IRS) [Member] | Indefinite Tax Period [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	121
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 9,400
Tax credit expiration year	2039
Various tax credits	$ 34
Minimum [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Tax credit expiration year	2034
Minimum [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Tax credit expiration year	2020
Maximum [Member] | Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Tax credit expiration year	2039
Maximum [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Tax credit expiration year	2023
Northwest Operations [Member]
Income Tax Contingency [Line Items]
Operating loss carryforward	$ 857