Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenue	$ 3,734	$ 3,495	$ 7,734	$ 6,998
Expense:
Compensation and benefits	2,135	1,998	4,359	4,003
Other operating expenses	908	796	1,776	1,545
Operating expenses	3,043	2,794	6,135	5,548
Operating income	691	701	1,599	1,450
Other net benefit credits	65	63	131	123
Interest income	3	2	6	4
Interest expense	(68)	(60)	(129)	(118)
Investment income	28	5	28	5
Income before income taxes	719	711	1,635	1,464
Income tax expense	183	204	403	379
Net income before non-controlling interests	536	507	1,232	1,085
Less: Net income attributable to non-controlling interests	5	6	11	15
Net income attributable to the Company	$ 531	$ 501	$ 1,221	$ 1,070
Net Income Per Share Attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 1.05	$ 0.98	$ 2.41	$ 2.08
Diluted net income per share attributable to the Company (usd per share)	$ 1.04	$ 0.96	$ 2.38	$ 2.05
Average number of shares outstanding:
Average number of shares outstanding - Basic	507	514	507	514
Average number of shares outstanding - Diluted	512	520	513	521
Shares outstanding at June 30,	505	513	505	513