Other Assets (Derivative Instruments Narrative) (Details ) - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020
Derivative [Line Items]
Derivative, terminated amount		$ 4,100,000,000
Swaps | Hedging
Derivative [Line Items]
Reclassification of hedge loss from AOCI	$ 57,000,000.0
Loss on derivative	$ 0