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	500	0	0	0	500
Other comprehensive income (loss), net of tax	10	0	0	10	0
Balance at Dec. 31, 2018	13,280	915	2	(7)	12,370
Balance at Sep. 30, 2018	13,054	915	2	(19)	12,156
Net income	214	0	0	0	214
Other comprehensive income (loss), net of tax	12	0	0	12	0
Balance at Dec. 31, 2018	13,280	915	2	(7)	12,370
Balance at Mar. 31, 2019	13,578	915	2	3	12,658
Net income	999	0	0	0	999
Other comprehensive income (loss), net of tax	12	0	0	12	0
Balance at Dec. 31, 2019	14,589	915	2	15	13,657
Balance at Sep. 30, 2019	14,411	915	2	18	13,476
Net income	181	0	0	0	181
Other comprehensive income (loss), net of tax	(3)	0	0	(3)	0
Balance at Dec. 31, 2019	$ 14,589	$ 915	$ 2	$ 15	$ 13,657