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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Loans:
Impaired loans	$ 837		$ 837		$ 1,022
Loss Impaired loans	(21)	$ (55)	(42)	$ (198)
Other assets:
Computer software, impairments	(1)	0	(4)	(5)
Gain (loss) on loans held for sale	(1)	0	(3)	(3)
Gain (loss) on energy investments	0		2
Gain (loss) on OREO		0		(1)
Gain (loss) on private equity investments		0		(12)
Gain (loss) on impairment of intangible assets		0		(1)
Gain (loss) on impairment of consolidated LIHC VIE	(3)	(27)	(11)	(27)
Loss, Total	(26)	(82)	(58)	(247)
Fair Value Measurements, Nonrecurring
Loans:
Impaired loans	97	194	97	194
Other assets:
Software	0	13	0	13
Loans held for sale	7	4	7	4
Renewable energy investment	0		0
OREO		3		3
Private equity investments		10		10
Intangible assets		0		0
Consolidated LIHC VIE	81	118	81	118
Total	185	342	185	342
Fair Value Measurements, Nonrecurring | Level 1
Loans:
Impaired loans	0	0	0	0
Other assets:
Software	0	0	0	0
Loans held for sale	0	0	0	0
Renewable energy investment	0		0
OREO		0		0
Private equity investments		0		0
Intangible assets		0		0
Consolidated LIHC VIE	0	0	0	0
Total	0	0	0	0
Fair Value Measurements, Nonrecurring | Level 2
Loans:
Impaired loans	0	0	0	0
Other assets:
Software	0	0	0	0
Loans held for sale	0	0	0	0
Renewable energy investment	0		0
OREO		0		0
Private equity investments		0		0
Intangible assets		0		0
Consolidated LIHC VIE	0	0	0	0
Total	0	0	0	0
Fair Value Measurements, Nonrecurring | Level 3
Loans:
Impaired loans	97	194	97	194
Other assets:
Software	0	13	0	13
Loans held for sale	7	4	7	4
Renewable energy investment	0		0
OREO		3		3
Private equity investments		10		10
Intangible assets		0		0
Consolidated LIHC VIE	81	118	81	118
Total	$ 185	$ 342	$ 185	$ 342