Share-based compensation (Pre-tax and After-tax Share-based Compensation Expense) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based Payment Arrangement, Expense, Tax Benefit		$ 12	$ 19	$ 48
Restricted stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax		224	235	259
Share-based compensation expense, after-tax		180	178	151
Stock options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Share-based compensation expense, pre-tax		42	50	41
Share-based compensation expense, after-tax	[1]	$ 39	$ 40	$ 26

[1] ⁽¹⁾  The windfall tax benefit recorded to Income tax expense in the Consolidated statement of operations was $12 million, $19 million, and $48 million for the years ended December 31, 2019, 2018, and 2017, respectively.