Fair Value Measurement and Fair Value of Financial Instruments - Assets Measured on Nonrecurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loans:
Impaired loans	$ 730	$ 865
Impaired loans, gain (loss)	106	34
Other assets:
Loans held for sale	0	0
Loans held for sale, gain (loss)	29	3
OREO	1	0
Private equity investments, gain (loss)	2
Renewable energy investments, gain (loss)	(2)	2
Software		0
Software, gain (loss)	4	22
Consolidated LIHC VIE		0
Consolidated LIHC VIE, gain (loss)	8	21
Total, gain (loss)	(151)	(78)
Level 2
Loans:
Impaired loans		0
Other assets:
Total	0	0
Level 1
Loans:
Impaired loans		0
Other assets:
Total	0	0
Fair Value, Measurements, Nonrecurring [Member]
Loans:
Impaired loans	151	79
Other assets:
Loans held for sale	85	0
Renewable energy investments	11
Renewable Energy Investment	0	0
Software	0	0
Consolidated LIHC VIE	43	66
Total	290	145
Fair Value, Measurements, Nonrecurring [Member] | Level 3
Loans:
Impaired loans	151	79
Other assets:
Loans held for sale	85	0
Renewable energy investments	11
Renewable Energy Investment	0	0
Software	0	0
Consolidated LIHC VIE	43	66
Total	290	145
Fair Value, Measurements, Nonrecurring [Member] | Level 2
Loans:
Impaired loans	0
Other assets:
Renewable energy investments	0
Renewable Energy Investment	0	0
Software	0
Consolidated LIHC VIE	0
Fair Value, Measurements, Nonrecurring [Member] | Level 1
Loans:
Impaired loans	0
Other assets:
Renewable energy investments	0
Renewable Energy Investment	0	$ 0
Software	0
Consolidated LIHC VIE	$ 0