Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 3,338	$ 3,246	$ 12,893	$ 12,951	$ 12,261
Expense:
Compensation and benefits			7,334	7,515	7,226
Other operating expenses			3,140	3,135	2,958
Operating expenses			10,474	10,650	10,184
Operating income	594	536	2,419	2,301	2,077
Interest income			13	21	18
Interest expense			(163)	(165)	(167)
Cost of extinguishment of debt			0	(137)	(24)
Investment income			38	37	69
Income before income taxes			2,307	2,057	1,973
Income tax expense			671	586	594
Income from continuing operations	380	269	1,636	1,471	1,379
Discontinued operations, net of tax	1	30	0	26	6
Net income before non-controlling interests			1,636	1,497	1,385
Less: Net income attributable to non-controlling interests			37	32	28
Net income attributable to the Company	$ 375	$ 294	$ 1,599	$ 1,465	$ 1,357
Basic Per Share Data:
Basic net income per share – Continuing operations (in dollars per share)	$ 0.72	$ 0.49	$ 3.01	$ 2.64	$ 2.46
Net income attributable to the Company (in dollars per share)	0.72	0.54	3.01	2.69	2.47
Diluted Per Share Data:
Continuing operations (in dollars per share)	0.71	0.48	2.98	2.61	2.42
Net income attributable to the Company (in dollars per share)	$ 0.71	$ 0.54	$ 2.98	$ 2.65	$ 2.43
Average number of shares outstanding
Basic (in shares)			531	545	549
Diluted (in shares)			536	553	558
Shares outstanding at December 31 (in shares)	522	540	522	540	547