Consolidated Statements of Shareholder's Equity - USD ($) $ in Millions	Total	Capital stock	Additional paid-in capital	Accumulated other comprehensive (loss) income	Retained earnings
Balance at Mar. 31, 2018	$ 12,880	$ 915	$ 2	$ (29)	$ 11,992
Cumulative-effect of change in accounting policy	(110)	0	0	12	(122)
Net income	286	0	0	0	286
Other comprehensive income (loss), net of tax	(2)	0	0	(2)	0
Balance at Sep. 30, 2018	13,054	915	2	(19)	12,156
Balance at Jun. 30, 2018	12,858	915	2	(21)	11,962
Net income	194	0	0	0	194
Other comprehensive income (loss), net of tax	2	0	0	2	0
Balance at Sep. 30, 2018	13,054	915	2	(19)	12,156
Balance at Mar. 31, 2019	13,578	915	2	3	12,658
Net income	818	0	0	0	818
Other comprehensive income (loss), net of tax	15	0	0	15	0
Balance at Sep. 30, 2019	14,411	915	2	18	13,476
Balance at Jun. 30, 2019	13,947	915	2	13	13,017
Net income	459	0	0	0	459
Other comprehensive income (loss), net of tax	5	0	0	5	0
Balance at Sep. 30, 2019	$ 14,411	$ 915	$ 2	$ 18	$ 13,476