Income Taxes Income Taxes (Schedule of Significant Components of Income Tax Expense) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)									$ (17)	$ 0	$ 0
Current Foreign Tax Expense (Benefit)									6	8	6
Current State and Local Tax Expense (Benefit)									53	9	3
Current Income Tax Expense (Benefit)									42	17	9
Deferred Federal Income Tax Expense (Benefit)									566	423	454
Deferred Foreign Income Tax Expense (Benefit)									0	0	1
Deferred State and Local Income Tax Expense (Benefit)									(27)	30	32
Deferred Income Tax Expense (Benefit)									539	453	487
Income Tax Expense (Benefit)	$ 231	$ 115	$ 122	$ 113	$ 134	$ 130	$ 56	$ 150	$ 581	$ 470	$ 496