Income Taxes Reconciliation of Statutory and Effective Tax Rates (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ (7.3)
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
U.S. Federal Statutory Income Tax Rate	21.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	2.80%	2.90%	2.50%
Tax law change	0.00%	(116.00%)	0.00%
Other, net	0.20%	(0.50%)	(0.20%)
Effective Tax Rate	24.00%	(78.60%)	37.30%
Effective Income Tax Rate Reconciliation, Percent, Before Impacts from Tax Rate Change	37.40%