Fair Value Measurement and Fair Value of Financial Instruments - Assets Measured on Nonrecurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair value measurements
Impairment of Loans Held for Sale	$ 3
Loans:
Impaired loans	833	$ 503
Loss Impaired loans	(95)	(37)
Impairment of Premises and Equipment	(6)
Other assets:
OREO	31	36
Loss on OREO	(2)	(6)
Impairment of Intangible Assets, Finite-lived	(4)
Loss on Private equity investments	(5)
Loss, Total	(115)	(43)
Fair Value Measurements, Nonrecurring
Fair value measurements
Loans Held-for-sale, Fair Value Disclosure	18
Loans:
Impaired loans	154	109
Property, Plant, and Equipment, Fair Value Disclosure	0
Other assets:
OREO	6	15
Private Equity Investments	7
Finite-lived Intangible Assets, Fair Value Disclosure	2
Total	187	124
Fair Value Measurements, Nonrecurring | Level 3
Fair value measurements
Loans Held-for-sale, Fair Value Disclosure	18
Loans:
Impaired loans	154	109
Property, Plant, and Equipment, Fair Value Disclosure	0
Other assets:
OREO	6	15
Private Equity Investments	7
Finite-lived Intangible Assets, Fair Value Disclosure	2
Total	$ 187	$ 124