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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Loans:
Impaired loans	$ 941		$ 941		$ 730
Gains Losses On Impaired Loans	12	$ (13)	(3)	$ (14)
Other assets:
Computer software, impairments	(1)	0	(3)	(2)
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		(8)		(8)
Other Assets	10,260		10,260		$ 9,620
Other Asset Impairment Charges	0		1	2
Total Gains Losses on Assets	2	(23)	(18)	(28)
Gain (Loss) on Energy Investments	0	(2)	(1)	(2)
Gains Losses on Loans Held for Sale	(9)		(9)
Fair Value Measurements, Nonrecurring
Loans:
Impaired loans	210	122	210	122
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		54		54
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		10		10
Other Assets	0		0
Total	324	188	324	188
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	114		114
Equity Method Investments, Fair Value Disclosure		2		2
Fair Value Measurements, Nonrecurring | Level 1
Loans:
Impaired loans	0	0	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
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	210	122	210	122
Other assets:
Software	0	0	0	0
Variable Interest Entity, Consolidated, Carrying Amount, Assets		54		54
Property, Plant and Equipment, Other, Net	0		0
Private equity investments		10		10
Other Assets	0		0
Total	324	188	324	188
Renewable Energy Investment	0		0
Loans Held-for-sale, Fair Value Disclosure	$ 114		$ 114
Equity Method Investments, Fair Value Disclosure		$ 2		$ 2