Derivatives and Hedging Activities - Effect of Fair Value and Cash Flow Hedges on Income (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense — Long-term debt		$ (120)	$ (92)
Interest income — Loans		1,066	940
Deposits		(202)	(91)
Other income	[1]	10	21
Interest Rate [Member] | Interest Expense, Long-Term Debt [Member] | Fair Value Hedging [Member]
Gain (Loss) on Fair Value Hedges Recognized in Earnings [Abstract]
Recognized on hedged items		(93)	71
Recognized on derivatives designated as hedging instruments		82	(69)
Net income (expense) recognized on fair value hedges		(11)	2
Interest Rate [Member] | Interest Expense, Long-Term Debt [Member] | Cash Flow Hedging [Member]
Cash Flow Hedges Derivative Instruments at Fair Value, Net [Abstract]
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		(1)	(1)
Net income (expense) recognized on cash flow hedges		(1)	(1)
Interest Rate [Member] | Interest Income [Member] | Fair Value Hedging [Member]
Gain (Loss) on Fair Value Hedges Recognized in Earnings [Abstract]
Recognized on hedged items		0	0
Recognized on derivatives designated as hedging instruments		0	0
Net income (expense) recognized on fair value hedges		0	0
Interest Rate [Member] | Interest Income [Member] | Cash Flow Hedging [Member]
Cash Flow Hedges Derivative Instruments at Fair Value, Net [Abstract]
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		(24)	(2)
Net income (expense) recognized on cash flow hedges		(24)	(2)
Interest Rate [Member] | Interest Expense, Deposits [Member] | Fair Value Hedging [Member]
Gain (Loss) on Fair Value Hedges Recognized in Earnings [Abstract]
Recognized on hedged items		0	0
Recognized on derivatives designated as hedging instruments		0	0
Net income (expense) recognized on fair value hedges		0	0
Interest Rate [Member] | Interest Expense, Deposits [Member] | Cash Flow Hedging [Member]
Cash Flow Hedges Derivative Instruments at Fair Value, Net [Abstract]
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		0	0
Net income (expense) recognized on cash flow hedges		0	0
Interest Rate [Member] | Other Income [Member] | Fair Value Hedging [Member]
Gain (Loss) on Fair Value Hedges Recognized in Earnings [Abstract]
Recognized on hedged items		0	0
Recognized on derivatives designated as hedging instruments		0	0
Net income (expense) recognized on fair value hedges		0	0
Interest Rate [Member] | Other Income [Member] | Cash Flow Hedging [Member]
Cash Flow Hedges Derivative Instruments at Fair Value, Net [Abstract]
Realized gains (losses) (pre-tax) reclassified from AOCI into net income		0	0
Net income (expense) recognized on cash flow hedges		$ 0	$ 0

[1] For the three months ended March 31, 2019, and March 31, 2018, net securities gains totaled less than $1 million. For the three months ended March 31, 2019, and March 31, 2018, we did not have any impairment losses related to securities.