Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Common stock, par value (USD per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	500,000,000	500,000,000
Common stock, shares issued (shares)	25,421,974	25,144,764
Treasury stock, shares (shares)	2,556,012	2,425,430
Accounts Receivable, Allowance for Credit Loss, Current	$ 8,906	$ 8,907
Unbilled Services, Allowance for Credit Losses	$ 3,640	$ 2,994