Fair Value, Measurements From Brokers or Third Party Pricing Services (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Financial assets
Trading debt securities		$ 70,208	$ 69,989
Available-for-sale, at fair value		265,983	269,912
Marketable equity securities		35,950	29,556
Equity securities	[1]	61,537	55,148
Derivative assets		40,050	34,560
Financial liabilities
Derivative liabilities		(38,116)	(32,047)
Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		15,319	13,348
Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		45,095	49,264
Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		161,301	160,203
Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		5,043	5,483
Brokers [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Derivative assets		0	0
Financial liabilities
Derivative liabilities		0	0
Other liabilities (2)		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		0	0
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities [Member]
Financial assets
Equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 1 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Derivative assets		0	0
Financial liabilities
Derivative liabilities		0	0
Other liabilities (2)		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		0	0
Available-for-sale, at fair value		45	45
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		45	45
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities [Member]
Financial assets
Equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 2 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Derivative assets		0	0
Financial liabilities
Derivative liabilities		0	0
Other liabilities (2)		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		0	0
Available-for-sale, at fair value		130	129
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		130	129
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities [Member]
Financial assets
Equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		0	0
Brokers [Member] | Fair Value, Inputs, Level 3 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Derivative assets		12	17
Financial liabilities
Derivative liabilities		(13)	(12)
Other liabilities (2)		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		534	899
Available-for-sale, at fair value		12,324	10,399
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		12,324	10,399
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Equity securities [Member]
Financial assets
Equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 1 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Derivative assets		0	0
Financial liabilities
Derivative liabilities		(2)	0
Other liabilities (2)		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		319	256
Available-for-sale, at fair value		250,844	255,780
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		2,995	2,949
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		44,642	48,377
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		161,260	160,162
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		41,947	44,292
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Equity securities [Member]
Financial assets
Equity securities		160	159
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		160	158
Third party pricing services [Member] | Fair Value, Inputs, Level 2 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		0	1
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Derivative assets		0	0
Financial liabilities
Derivative liabilities		0	0
Other liabilities (2)		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Debt securities [Member]
Financial assets
Trading debt securities		0	0
Available-for-sale, at fair value		742	842
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. Treasury and federal agencies [Member]
Financial assets
Available-for-sale, at fair value		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Securities of U.S. states and political subdivisions [Member]
Financial assets
Available-for-sale, at fair value		38	43
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed securities [Member]
Financial assets
Available-for-sale, at fair value		41	41
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Other debt securities [Member]
Financial assets
Available-for-sale, at fair value		663	758
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Equity securities [Member]
Financial assets
Equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Marketable equity securities [Member]
Financial assets
Marketable equity securities		0	0
Third party pricing services [Member] | Fair Value, Inputs, Level 3 [Member] | Nonmarketable equity securities [Member]
Financial assets
Nonmarketable equity securities		$ 0	$ 0

[1] (1) Parenthetical amounts represent assets and liabilities that we are required to carry at fair value or have elected the fair value option.