Shareholders' Equity - Narrative (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
	Mar. 09, 2016	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Preferred shares outstanding (in shares)		126,000	126,000		107,000
Shares repurchased			$ 193	$ 51
Repurchase Plan 2015 [Member]
Class of Stock [Line Items]
Shares repurchased		$ 160
Shares repurchased, Shares		4,300,000
Series H non-cumulative perpetual preferred stock
Class of Stock [Line Items]
Issued perpetual preferred stock	$ 465
Stated dividend rate	5.625%
Net proceeds on issuance of stock	$ 450
Preferred shares outstanding (in shares)	18,600