Employee Benefit Plans - Stock unit activity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary of stock unit activity
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	16,922,525
RSU Stock Settled [Member]
Summary of stock unit activity
Stock Units, Outstanding Beginning of year	6,223,046
Stock Units, Granted	2,890,840
Stock Units, Forfeited / Cancelled	(127,181)
Stock Units, Issued	(2,554,720)
Stock Units, Outstanding End of year	6,431,985	6,223,046
Not Vested at End of Year	4,230,413
Weighted-Average Grant-Date Fair Value, beginning of year	$ 55.99
Weighted-Average Grant-Date Fair Value, Granted	57.40	$ 67.77	$ 52.45
Weighted-Average Grant-Date Fair Value, Forfeited / Cancelled	55.84
Weighted-Average Grant-Date Fair Value, Issued	50.16
Weighted-Average Grant-Date Fair Value, ending of year	58.94	$ 55.99
Weighted-Average Grant-Date Fair Value Not Vested, ending of year	$ 59.01
Total Fair Value, Issued	$ 143	$ 225	$ 154
Employee Benefit Plans Additional (Textual) [Abstract]
Unrecognized compensation cost from stock options	$ 101
Weighted average period of recognition of unvested options, in months	1 year 8 months 15 days
Longest weighted-average period of recognition of unvested options, in months	2 years 1 month 20 days
Total Fair Value, Issued	$ 143	$ 225	$ 154
RSU Cash Settled [Member]
Summary of stock unit activity
Stock Units, Outstanding Beginning of year	596,991
Stock Units, Granted	24,437
Stock Units, Forfeited / Cancelled	(5,622)
Stock Units, Issued	(1,191)
Stock Units, Outstanding End of year	614,615	596,991
Not Vested at End of Year	121,696
Weighted-Average Grant-Date Fair Value, beginning of year	$ 64.54
Weighted-Average Grant-Date Fair Value, Granted	41.59	$ 68.20	$ 53.68
Weighted-Average Grant-Date Fair Value, Forfeited / Cancelled	40.01
Weighted-Average Grant-Date Fair Value, Issued	40.20
Weighted-Average Grant-Date Fair Value, ending of year	39.95	$ 64.54
Weighted-Average Grant-Date Fair Value Not Vested, ending of year	$ 39.95
Total Fair Value, Issued	$ 0	$ 6	$ 1
Employee Benefit Plans Additional (Textual) [Abstract]
Unrecognized compensation cost from stock options	$ 1
Weighted average period of recognition of unvested options, in months	1 year
Longest weighted-average period of recognition of unvested options, in months	1 year 1 month 13 days
Total Fair Value, Issued	$ 0	$ 6	$ 1