Income Taxes (Income Tax Provision) (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									$ 112	$ 161	$ 182
Current, State									19	22	31
Current, Foreign									44	36	32
Current Income Tax Provision									175	219	245
Deferred, Federal									(399)	80	34
Deferred, State									(3)	16	8
Deferred, Foreign									(2)	(2)	(2)
Deferred Income Tax Provision									(404)	94	40
Provision for income taxes	$ (383)	$ 98	$ 30	$ 27	$ 62	$ 98	$ 87	$ 65	$ (229)	$ 313	$ 285