Shareholders' Equity - Schedule of Preferred Shares Outstanding (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Class of Stock [Line Items]
Proceeds from issuance of preferred stock, net	$ 0	$ 493
Series C Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	20,000,000
Liquidation preference per share (USD per share)	$ 25
Series C Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock, net	$ 488
Series D Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	30,000,000
Liquidation preference per share (USD per share)	$ 25
Series D Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock, net	$ 742
Series E Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	30,000,000
Liquidation preference per share (USD per share)	$ 25
Series E Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock, net	$ 728
Series F Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	750,000
Liquidation preference per share (USD per share)	$ 1,000
Series F Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	1.00%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock, net	$ 742
Series G Preferred Stock, Depository Share
Class of Stock [Line Items]
Depositary shares issued (shares)	20,000,000
Liquidation preference per share (USD per share)	$ 25
Series G Preferred Stock
Class of Stock [Line Items]
Ownership Interest Per Depositary Share	0.025%
Liquidation preference per share (USD per share)	$ 100,000
Proceeds from issuance of preferred stock, net	$ 493