Fair Value Measurement and Fair Value of Financial Instruments - Financial Assets Measured at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Loans:
Impaired loans	$ 781		$ 781		$ 730
Gains Losses On Impaired Loans	(17)	$ (59)	(20)	$ (73)
Goodwill	1,764		1,764		3,301
Impairment losses	(1,614)	0	(1,614)	0
Other assets:
Computer software, impairments	0	(1)	(3)	(3)
Impairment of Premises and Equipment	0		(1)
Gains Losses of Private Equity Investments		0
Gains Losses of Consolidated Variable Interest Entity Low Income Housing Credit Investments		0		(8)
Other Assets	10,002		10,002		$ 9,620
Other Asset Impairment Charges	0		1	2
Total Gains Losses on Assets	(1,637)	(60)	(1,655)	(88)
Gain (Loss) on Energy Investments	0	0	(1)	(2)
Gains Losses on Loans Held for Sale	(6)		(15)
Fair Value Measurements, Nonrecurring
Loans:
Impaired loans	36	183	36	183
Goodwill	1,764		1,764
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		48		48
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		10		10
Other Assets	0		0
Total	2,060	243	2,060	243
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	260		260
Equity Method Investments, Fair Value Disclosure		2		2
Fair Value Measurements, Nonrecurring | Level 1
Loans:
Impaired loans	0	0	0	0
Goodwill	0		0
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		0		0
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		0		0
Other Assets	0		0
Total	0	0	0	0
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	0		0
Equity Method Investments, Fair Value Disclosure		0		0
Fair Value Measurements, Nonrecurring | Level 2
Loans:
Impaired loans	0	0	0	0
Goodwill	0		0
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		0		0
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		0		0
Other Assets	0		0
Total	0	0	0	0
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	0		0
Equity Method Investments, Fair Value Disclosure		0		0
Fair Value Measurements, Nonrecurring | Level 3
Loans:
Impaired loans	36	183	36	183
Goodwill	1,764		1,764
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		48		48
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		10		10
Other Assets	0		0
Total	2,060	243	2,060	243
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	$ 260		$ 260
Equity Method Investments, Fair Value Disclosure		$ 2		$ 2