Income and Other Taxes - Reconciliation of Statutory Tax Rate to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21.00%	21.00%	35.00%
Nondeductible expenses	1.30%	3.70%	1.30%
Effect of tax law changes	(4.60%)	14.50%	76.20%
Change in valuation allowance for deferred tax assets	2.00%	0.60%	1.10%
State taxes, net of federal benefit	3.50%	2.30%	3.60%
Audit and other tax return adjustments	0.60%	(1.80%)	(9.40%)
Tax-exempt income, credits and incentives	(2.10%)	(2.20%)	(3.20%)
Foreign rate differential adjusted for U.S. taxation of foreign profits	0.10%	4.80%	(16.50%)
Other	0.00%	2.10%	1.00%
Effective Income Tax Rate	21.80%	45.00%	89.10%
Income Taxes Paid	$ 94	$ 80	$ 84