Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 3,495	$ 3,376	$ 6,998	$ 6,712
Expense:
Compensation and benefits	1,935	1,872	3,880	3,726
Other operating expenses	796	778	1,545	1,527
Operating expenses	2,731	2,650	5,425	5,253
Operating income	764	726	1,573	1,459
Interest income	2	2	4	4
Interest expense	(60)	(48)	(118)	(94)
Investment income (loss)	5	1	5	(2)
Income before income taxes	711	681	1,464	1,367
Income tax expense	204	201	379	397
Net income before non-controlling interests	507	480	1,085	970
Less: Net income attributable to non-controlling interests	6	8	15	17
Net income attributable to the Company	$ 501	$ 472	$ 1,070	$ 953
Net Income Per Share Attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 0.98	$ 0.91	$ 2.08	$ 1.83
Diluted net income per share attributable to the Company (usd per share)	$ 0.96	$ 0.90	$ 2.05	$ 1.81
Average number of shares outstanding:
Average number of shares outstanding - Basic	514	521	514	521
Average number of shares outstanding - Diluted	520	525	521	526
Shares outstanding at June 30,	513	519	513	519