Guarantor Financial Information (CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (LOSS)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Net operating revenues	$ 8,239	$ 8,549	$ 24,323	$ 24,808
Cost of Services (exclusive of depreciation and amortization included below)	1,733	1,925	5,140	6,125
Cost of Products (exclusive of depreciation and amortization included below)	1,673	1,985	4,622	5,097
Net operating expenses
Selling, general and administrative	2,108	2,080	6,059	5,992
Severance and exit costs	13	19	13	30
Depreciation	1,977	1,837	5,693	5,227
Amortization	196	255	628	813
Other, net	(188)	137	(323)	230
Total costs and expenses	7,512	8,238	21,832	23,514
Operating Income	727	311	2,491	1,294
Other (expense) income
Interest Income	14	12	66	37
Interest Expense	(581)	(619)	(1,789)	(1,864)
(Losses) earnings of Subsidiaries	0	0	0	0
Other nonoperating income (expense), excluding interest income	(56)	(72)	(116)	(104)
Nonoperating Expense	(623)	(679)	(1,839)	(1,931)
Loss (income) before income taxes	104	(368)	652	(637)
Income tax benefit	7,052	(111)	6,662	(286)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,156	(479)	7,314	(923)
Net Income (Loss) Attributable to Noncontrolling Interest	6	0	6	0
Net (loss) income	7,162	(479)	7,320	(923)
Other Comprehensive Income (Loss), Net of Tax	26	(5)	38	2
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,182		7,352
Comprehensive (loss) income	7,182	(484)	7,352	(921)
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	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	(643)	(233)	(1,320)	(674)
Interest Expense	643	233	1,320	674
(Losses) earnings of Subsidiaries	(14,250)	517	(15,042)	603
Other nonoperating income (expense), excluding interest income	0	0	0	0
Nonoperating Expense	(14,250)	517	(15,042)	603
Loss (income) before income taxes	(14,250)	517	(15,042)	603
Income tax benefit	0	0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(14,250)		(15,042)
Net Income (Loss) Attributable to Noncontrolling Interest	0		0
Net (loss) income	(14,250)	517	(15,042)	603
Other Comprehensive Income (Loss), Net of Tax	(32)	9	(56)	(5)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(14,282)		(15,098)
Comprehensive (loss) income		526		598
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	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	198	198	593	593
Interest Expense	(198)	(198)	(593)	(593)
(Losses) earnings of Subsidiaries	7,162	(479)	7,320	(923)
Other nonoperating income (expense), excluding interest income	0	0	0	0
Nonoperating Expense	7,162	(479)	7,320	(923)
Loss (income) before income taxes	7,162	(479)	7,320	(923)
Income tax benefit	0	0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,162		7,320
Net Income (Loss) Attributable to Noncontrolling Interest	0		0
Net (loss) income	7,162	(479)	7,320	(923)
Other Comprehensive Income (Loss), Net of Tax	26	(5)	38	2
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,188		7,358
Comprehensive (loss) income		(484)		(921)
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	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	458	43	783	105
Interest Expense	(382)	(409)	(1,171)	(1,271)
(Losses) earnings of Subsidiaries	7,088	(38)	7,722	320
Other nonoperating income (expense), excluding interest income	(2)	(75)	(69)	(77)
Nonoperating Expense	7,162	(479)	7,265	(923)
Loss (income) before income taxes	7,162	(479)	7,320	(923)
Income tax benefit	0	0	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,162		7,320
Net Income (Loss) Attributable to Noncontrolling Interest	0		0
Net (loss) income	7,162	(479)	7,320	(923)
Other Comprehensive Income (Loss), Net of Tax	26	(5)	38	2
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,188		7,358
Comprehensive (loss) income		(484)		(921)
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	8,239	8,549	24,323	24,808
Cost of Services (exclusive of depreciation and amortization included below)	1,733	1,925	5,140	6,125
Cost of Products (exclusive of depreciation and amortization included below)	1,673	1,985	4,622	5,097
Net operating expenses
Selling, general and administrative	2,108	2,080	6,059	5,992
Severance and exit costs	13	19	13	30
Depreciation	1,977	1,837	5,693	5,227
Amortization	196	255	628	813
Other, net	(188)	137	(268)	230
Total costs and expenses	7,512	8,238	21,887	23,514
Operating Income	727	311	2,436	1,294
Other (expense) income
Interest Income	1	4	10	13
Interest Expense	(644)	(245)	(1,345)	(674)
(Losses) earnings of Subsidiaries	0	0	0	0
Other nonoperating income (expense), excluding interest income	(54)	3	(47)	(27)
Nonoperating Expense	(697)	(238)	(1,382)	(688)
Loss (income) before income taxes	30	73	1,054	606
Income tax benefit	7,052	(111)	6,662	(286)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	7,082		7,716
Net Income (Loss) Attributable to Noncontrolling Interest	6		6
Net (loss) income	7,088	(38)	7,722	320
Other Comprehensive Income (Loss), Net of Tax	6	(4)	18	3
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 7,088		$ 7,734
Comprehensive (loss) income		$ (42)		$ 323