Summary of Significant Accounting Principles and Practices - Schedule of Topic 606 Impact on the Income Statement (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue
Total revenue	$ 2,770	$ 2,349	$ 2,561	$ 3,090	$ 2,909	$ 2,340	$ 2,368	$ 2,381	$ 10,770	$ 9,998	$ 9,409
Expenses
Compensation and benefits									6,103	6,003	5,514
Other general expenses									1,500	1,272	1,036
Other income (expense)									(25)	(125)	(137)
Income taxes									146	$ 250	$ 148
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue
Total revenue									(61)
Expenses
Compensation and benefits									51
Other general expenses									(1)
Other income (expense)									1
Income taxes									(34)
Calculated under Revenue Guidance in Effect before Topic 606
Revenue
Total revenue									10,709
Expenses
Compensation and benefits									6,154
Other general expenses									1,499
Other income (expense)									(24)
Income taxes									$ 112