Quarterly Financial Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Selected Quarterly Financial Information [Abstract]
Goodwill, Impairment Loss									$ 2,000,000,000
Revenues	$ 8,441,000,000	$ 8,601,000,000	$ 8,433,000,000	$ 8,125,000,000	$ 8,083,000,000	$ 8,239,000,000	$ 7,927,000,000	$ 8,157,000,000	33,600,000,000	$ 32,406,000,000	$ 33,347,000,000
Operating income (loss)	(1,674,000,000)	479,000,000	778,000,000	815,000,000	236,000,000	727,000,000	601,000,000	1,163,000,000	398,000,000	2,727,000,000	1,764,000,000
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(2,178,000,000)	(145,000,000)	207,000,000	173,000,000	63,000,000	7,156,000,000	(48,000,000)	206,000,000
Net Income (Loss) Attributable to Parent	$ (2,174)	$ (141)	$ 196	$ 176	$ 0	$ 0	$ 0	$ 0	$ (1,943,000,000)	$ 7,389,000,000	$ (1,206,000,000)
Earnings Per Share, Basic	$ (0.53)	$ (0.03)	$ 0.05	$ 0.04	$ 0.02	$ 1.79	$ (0.01)	$ 0.05	$ (0.48)	$ 1.85	$ (0.30)
Earnings Per Share, Diluted	$ (530,000)	$ (30,000)	$ 50,000	$ 40,000	$ 20,000	$ 1,760,000	$ (10,000)	$ 50,000	$ (0.48)	$ 1.81	$ (0.30)