Summary of Significant Accounting Policies (Amounts Attributable to Controlling Interests) (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
Net Income (Loss) Attributable to Parent [Abstract]
Income (Loss) from Continuing Operations	$ 705	$ 957	$ 691	$ 717	$ 376	$ 1,001	$ 624	$ 577	$ 3,070	$ 2,578	$ 2,654
Income (Loss) from Continuing Operations Attributable to Noncontrolling Interests									5	7	9
Income (Loss) from Continuing Operations Attributable to Parent									3,065	2,571	2,645
Income (Loss) From Discontinued Operations, net of tax	(2)	(2)	(2)		(598)	180	(112)	122	(6)	(408)	177
Income (Loss) from Discontinued Operations Attributable to Noncontrolling Interest, net of tax										11	6
(Loss) Income from Discontinued Operations Attributable to Parent, net of tax										(419)	171
Net income (loss)	703	955	689	717	(222)	1,181	512	699	3,064	2,170	2,831
Net Income Attributable to Noncontrolling Interest									5	18	15
Net Income (Loss) Attributable to Parent	$ 703	$ 954	$ 686	$ 716	$ (227)	$ 1,176	$ 509	$ 694	$ 3,059	$ 2,152	$ 2,816