Condensed Consolidated Statements of Shareholders' Equity (Parentheticals) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Treasury shares held in trust (in shares)	1	1	1	1
Treasury share held in trust	$ 29	$ 29	$ 29	$ 29
Common stock	17	17	17	$ 17
Decrease in retained earnings		$ (51,203)	$ (49,640)
Accounting Standards Update 2016-13
Decrease in retained earnings	$ 3
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13