Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes (Textuals) [Abstract]
Effective income tax rate (percent)		19.10%	32.40%	120.30%
Remeasurement of deferred taxes		$ 0	$ 24	$ 1,193
Valuation allowances		5	21	11
Unrecognized tax benefits		164	158	80	$ 84
Increase resulting from nondeductible interest		14
Increase in worthless stock deduction reserve		6
Decrease resulting from nondeductible interest			11
Decrease for lapse in statute		4	2	$ 6
Unrecognized tax benefits that would impact future tax rates		151
Unrecognized tax benefits, portion expected to be resolved in the next fiscal year		59
Unrecognized tax benefits that would impact effective tax rate		57
Federal
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards, not subject to expiration		9
Federal | Begin To Expire in 2031
Income Taxes (Textuals) [Abstract]
Pre-tax net operating loss carryforwards		2,100
Operating loss carryforwards, subject to expiration		441
State and Local
Income Taxes (Textuals) [Abstract]
Pre-tax net operating loss carryforwards		6,800
Operating loss carryforwards, subject to expiration		361
Pre-tax net operating loss carryforwards expected to utilized		1,500
Operating loss carryforwards expected to utilized, net of tax		103
Tax deferred expense, net of tax		$ 62
Decrease for lapse in statute			$ 3
West Virginia | State and Local
Income Taxes (Textuals) [Abstract]
Valuation allowances	$ 126