New Accounting Pronouncements (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2019	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in cash provided by operating activities	$ (10,464)	$ (16,324)
Increase (decrease) in cash provided by investing activities	20,521	21,819
Increase (decrease) in cash provided by financing activities	$ (10,680)	(5,850)
Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in cash provided by operating activities		(8)
Increase (decrease) in cash provided by investing activities		(3)
Increase (decrease) in cash provided by financing activities		(5)
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (decrease) in cash provided by investing activities		$ (106)
Retained Earnings [Member] | Accounting Standards Update 2016-01, Equity Investments Previously Measured at Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ 10
Retained Earnings [Member] | Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				(4)
Retained Earnings [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				91
Other assets [Member] | Accounting Standards Update 2016-01, Equity Investments Previously Measured at Cost [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				10
AOCI Attributable to Parent [Member] | Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				4
AOCI Attributable to Parent [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				(91)
To Other Assets from Trading Assets [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				12
To Other Assets From Securities Available-for-sale [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				177
Trading Assets [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				(12)
Available-for-sale securities [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ (177)
Scenario, Forecast [Member] | Retained Earnings [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption			$ 27
Minimum [Member] | Scenario, Forecast [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset			650
Operating Lease, Liability			650
Maximum [Member] | Scenario, Forecast [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset			700
Operating Lease, Liability			$ 700