Income Taxes, Tax Credits and Loss Carryforwards (Details) - U.S. state income tax credits [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards
U.S. state NOLs (gross amount)	$ 9,441
U S State Income Tax Credits Limited [Member]
Operating Loss Carryforwards
U.S. state income tax credits	76
U S State Income Tax Credits Unlimited [Member]
Operating Loss Carryforwards
U.S. state income tax credits	$ 11
Minimum [Member]
Operating Loss Carryforwards
U.S state NOL (gross amount)	Dec. 31, 2018
Minimum [Member] | U S State Income Tax Credits Limited [Member]
Operating Loss Carryforwards
U.S state income tax credits	Dec. 31, 2018
Maximum [Member]
Operating Loss Carryforwards
U.S state NOL (gross amount)	Dec. 31, 2037
Maximum [Member] | U S State Income Tax Credits Limited [Member]
Operating Loss Carryforwards
U.S state income tax credits	Dec. 31, 2031