Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	1 Months Ended		2 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	May 31, 2021	Apr. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Apr. 30, 2021	Jun. 30, 2020
Successor [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit)	$ 55
Successor [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 13
Interest cost on projected benefit obligation			18
Expected return on plan assets			(31)
Successor [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			3
Interest cost on projected benefit obligation			5
Amortization of prior service cost (credit)	$ 55		(1)
Amortization of unrecognized (gain) loss			13
Net periodic benefit cost			20
Total benefit cost			$ 20
Predecessor [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 8		$ 24	$ 32	$ 49
Interest cost on projected benefit obligation		8		28	31	58
Expected return on plan assets		(16)		(39)	(61)	(89)
Amortization of unrecognized (gain) loss		6		30	24	47
Net periodic benefit cost		6		43	26	65
Pension settlement costs				56		159
Gain on disposal, net				(50)		(50)
Total benefit cost		6		49	26	174
Predecessor [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2		5	7	10
Interest cost on projected benefit obligation		2		8	9	16
Amortization of prior service cost (credit)		(3)		(8)	(10)	(16)
Amortization of unrecognized (gain) loss		2		1	5	3
Net periodic benefit cost		3		6	11	13
One-time gain on sale				(24)		(24)
Total benefit cost		$ 3		$ (18)	$ 11	$ (11)