Guarantor Financial Information (CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (LOSS)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Income Statements, Captions [Line Items]
Net operating revenues	$ 7,927	$ 8,247	$ 16,084	$ 16,259
Cost of Services (exclusive of depreciation and amortization included below)	1,698	2,101	3,407	4,200
Cost of Products (exclusive of depreciation and amortization included below)	1,404	1,693	2,949	3,112
Net operating expenses
Selling, general and administrative	2,013	1,995	3,951	3,912
Severance and exit costs	0	(5)	0	11
Depreciation	1,885	1,710	3,716	3,390
Amortization	209	271	432	558
Other, net	117	(140)	(135)	93
Total costs and expenses	7,326	7,625	14,320	15,276
Operating Income	601	622	1,764	983
Other (expense) income
Interest Income	33	15	52	25
Interest Expense	(595)	(630)	(1,208)	(1,245)
(Losses) earnings of Subsidiaries	0	0	0	0
Other nonoperating income (expense), excluding interest income	11	(30)	(60)	(32)
Nonoperating Expense	(551)	(645)	(1,216)	(1,252)
Loss (income) before income taxes	50	(23)	548	(269)
Income tax benefit	(98)	(119)	(390)	(175)
Net (loss) income	(48)	(142)	158	(444)
Other Comprehensive Income (Loss), Net of Tax	16	8	12	7
Comprehensive (loss) income	(32)	(134)	170	(437)
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0	0	0
Cost of Products (exclusive of depreciation and amortization included below)	0	0	0	0
Net operating expenses
Selling, general and administrative	0	0	0	0
Severance and exit costs		0	0	0
Depreciation	0	0	0	0
Amortization	0	0	0	0
Other, net	0	0	0	0
Total costs and expenses	0	0	0	0
Operating Income	0	0	0	0
Other (expense) income
Interest Income	(449)	(222)	(677)	(441)
Interest Expense	449	222	677	441
(Losses) earnings of Subsidiaries	(62)	(122)	(792)	86
Other nonoperating income (expense), excluding interest income	0	0	0	0
Nonoperating Expense	(62)	(122)	(792)	86
Loss (income) before income taxes	(62)	(122)	(792)	86
Income tax benefit	0	0	0	0
Net (loss) income	(62)	(122)	(792)	86
Other Comprehensive Income (Loss), Net of Tax	(23)	(14)	(24)	(14)
Comprehensive (loss) income	(85)	(136)	(816)	72
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0	0	0
Cost of Products (exclusive of depreciation and amortization included below)	0	0	0	0
Net operating expenses
Selling, general and administrative	0	0	0	0
Severance and exit costs		0	0	0
Depreciation	0	0	0	0
Amortization	0	0	0	0
Other, net	0	0	0	0
Total costs and expenses	0	0	0	0
Operating Income	0	0	0	0
Other (expense) income
Interest Income	197	197	395	395
Interest Expense	(197)	(197)	(395)	(395)
(Losses) earnings of Subsidiaries	(48)	(142)	158	(444)
Other nonoperating income (expense), excluding interest income	0	0	0	0
Nonoperating Expense	(48)	(142)	158	(444)
Loss (income) before income taxes	(48)	(142)	158	(444)
Income tax benefit	0	0	0	0
Net (loss) income	(48)	(142)	158	(444)
Other Comprehensive Income (Loss), Net of Tax	16	8	12	7
Comprehensive (loss) income	(32)	(134)	170	(437)
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0	0	0
Cost of Products (exclusive of depreciation and amortization included below)	0	0	0	0
Net operating expenses
Selling, general and administrative	0	0	0	0
Severance and exit costs		0	0	0
Depreciation	0	0	0	0
Amortization	0	0	0	0
Other, net	0	0	(55)	0
Total costs and expenses	0	0	(55)	0
Operating Income	0	0	55	0
Other (expense) income
Interest Income	280	34	325	62
Interest Expense	(438)	(439)	(789)	(862)
(Losses) earnings of Subsidiaries	110	264	634	358
Other nonoperating income (expense), excluding interest income	0	(1)	(67)	(2)
Nonoperating Expense	(48)	(142)	103	(444)
Loss (income) before income taxes	(48)	(142)	158	(444)
Income tax benefit	0	0	0	0
Net (loss) income	(48)	(142)	158	(444)
Other Comprehensive Income (Loss), Net of Tax	16	8	12	7
Comprehensive (loss) income	(32)	(134)	170	(437)
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	7,927	8,247	16,084	16,259
Cost of Services (exclusive of depreciation and amortization included below)	1,698	2,101	3,407	4,200
Cost of Products (exclusive of depreciation and amortization included below)	1,404	1,693	2,949	3,112
Net operating expenses
Selling, general and administrative	2,013	1,995	3,951	3,912
Severance and exit costs		(5)	0	11
Depreciation	1,885	1,710	3,716	3,390
Amortization	209	271	432	558
Other, net	117	(140)	(80)	93
Total costs and expenses	7,326	7,625	14,375	15,276
Operating Income	601	622	1,709	983
Other (expense) income
Interest Income	5	6	9	9
Interest Expense	(409)	(216)	(701)	(429)
(Losses) earnings of Subsidiaries	0	0	0	0
Other nonoperating income (expense), excluding interest income	11	(29)	7	(30)
Nonoperating Expense	(393)	(239)	(685)	(450)
Loss (income) before income taxes	208	383	1,024	533
Income tax benefit	(98)	(119)	(390)	(175)
Net (loss) income	110	264	634	358
Other Comprehensive Income (Loss), Net of Tax	7	6	12	7
Comprehensive (loss) income	$ 117	$ 270	$ 646	$ 365