Derivative Financial Instruments Hedged Items in Fair Value Hedging Relationships (Details) - Fair Value Hedging [Member]	3 Months Ended
	Mar. 31, 2018 USD ($)
Long-term Debt [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Carrying Amount of Assets	$ 5,658,000,000
Long-term Debt [Member] | Designated as Hedging Instrument [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Hedged Asset, Cumulative Basis Adjustment	(148,000,000)
Long-term Debt [Member] | Not Designated as Hedging Instrument [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Hedged Asset, Cumulative Basis Adjustment	(41,000,000)
Brokered Time Deposits [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Carrying Amount of Assets	29,000,000
Brokered Time Deposits [Member] | Designated as Hedging Instrument [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Hedged Asset, Cumulative Basis Adjustment	0
Brokered Time Deposits [Member] | Not Designated as Hedging Instrument [Member]
Hedged Items in Fair Value Hedging Relationships [Line Items]
Hedged Asset, Cumulative Basis Adjustment	$ 0