Shareholders' Equity - Shares Repurchased and Reissued (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Aug. 31, 2020
Share repurchases
Repurchase of common shares	$ 586	$ 341	$ 1,624	$ 1,135
Stock repurchase program, authorized amount					$ 2,500
Remaining balance under stock repurchase program	$ 932		$ 932
Shares surrendered upon vesting for income tax obligation			0.3	0.3
Income tax obligations paid on vesting date			$ 69	$ 51
Number of shares reacquired through net settlement options			0.9	0.7
Aggregate value of shares reacquired through net settlement options			$ 209	$ 128
Treasury shares reissued for restricted stock award grants, performance share units and issuance of shares vested under advisor deferred compensation plans			0.4	0.5
Share repurchase authorization
Share repurchases
Repurchase of common shares (in shares)			5.5	6.3
Repurchase of common shares			$ 1,300	$ 956