Borrowings and Other Obligations (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Aug. 04, 2020	Dec. 12, 2019
Short-term Debt [Line Items]
Debt instrument, unused borrowing capacity, amount			$ 42		$ 42
Short-term Debt			211		211		$ 13
Minimum Liquidity Covenant			300	$ 175	300
Interest Payable			77		77		34
Payment for Debt Extinguishment or Debt Prepayment Cost					22	$ 0
Gain (Loss) on Extinguishment of Debt, before Write off of Debt Issuance Cost					37	0
Proceeds from Issuance of Secured Debt					491	457
permitted borrowing			400
Minimum Book Value of Pledged Assets for Covenants under LC Credit Agreement			1,000	$ 1,250
Minimum aggregate liquidity requirment covenant in order to redeem debt			400
Amount of debt redeemable if minimum liquidity requirement met			500
LC Credit Agreement Letters of Credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount			173		173
Other short-term bank loans
Short-term Debt [Line Items]
Short-term Debt			0		0		4
Current Portion of Exit Notes and Finance Lease			211		211		9
Committed Letters of Credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount						$ 329
Letters of credit outstanding, cash collateral			152		152
Committed letters of credit
Short-term Debt [Line Items]
Letters of credit outstanding, amount			156		156
Exit Notes
Short-term Debt [Line Items]
Current Portion of Exit Notes and Finance Lease			200		200
Exit Notes | Subsequent Event
Short-term Debt [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost		$ 6
Repayments of Debt	$ 200
Interest paid on early redemption of debt		$ 8
Amended LC Credit Agreement [Member]
Short-term Debt [Line Items]
Credit agreement, maximum capacity			215		215
Senior Notes
Short-term Debt [Line Items]
Long-term Debt			1,898		1,898		2,098
Senior Notes | Senior Notes 8.75 Percent Due 2024
Short-term Debt [Line Items]
Stated interest rate on debt								8.75%
Face amount of debt								$ 500
Senior Notes | Exit Notes, 11.00 Percent Due 2024
Short-term Debt [Line Items]
Stated interest rate on debt									11.00%
Face amount of debt									$ 2,100
Senior Notes | Senior Notes 6.5 Percent Due 2028
Short-term Debt [Line Items]
Stated interest rate on debt								6.50%
Face amount of debt								$ 500
Secured Debt
Short-term Debt [Line Items]
Long-term Debt			$ 488		$ 488		$ 0