Investments (Equity Method Investments) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 6,048			$ 6,006
Proceeds from collateralized obligation			$ 5,200
Collateralized obligation	5,168			5,168
Level 2 [Member]
Schedule of Equity Method Investments [Line Items]
Collateralized obligation	5,200			5,200
Fair value of collateralized obligation	5,200			5,200
Atairos [Member]
Schedule of Equity Method Investments [Line Items]
Cash capital contributions for equity method investments	12	$ 12
Equity method investment	$ 3,900			$ 3,900