Share-based compensation (Pre-tax and After-tax Share-based Compensation Expense) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Payment Arrangement, Expense, Tax Benefit		$ 10	$ 12	$ 19
Restricted stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax		210	224	235
Share-based compensation expense, after-tax		164	180	178
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax		45	42	50
Share-based compensation expense, after-tax	[1]	$ 38	$ 39	$ 40

[1] The windfall tax benefit recorded to Income tax expense in the Consolidated statement of operations was $10 million, $12 million, and $19 million for the years ended December 31, 2020, 2019, and 2018, respectively.