Shareholders' Equity - Summary of Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Equity-based compensation expense	$ 141	$ 132	$ 115
Income tax benefit from equity-based compensation expense	34	34	43
Intrinsic value of options exercised, and RSUs and PSUs that vested during the year	260	261	159
Grant date fair value of equity-based awards that vested during the year	139	116	98
Unrecognized compensation cost related to equity-based awards	$ 135	$ 132	$ 109
Weighted-average life over which compensation cost is expected to be recognized	2 years 4 months 24 days	2 years 4 months 24 days	2 years 3 months 18 days