Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 15, 2016	Jan. 31, 2015	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Bridge Loan [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Bridge loan		$ 4,500		$ 4,500	$ 4,500
Debt instrument, term		364 days		364 days	364 days
Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued		30,000,000
Share price		$ 23.00
Proceeds from issuance of shares		$ 669
Depositary Shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued		34,500,000
Proceeds from issuance of shares		$ 1,700
Depositary shares conversion rate		5.00%
Liquidation preference per share		$ 50
Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Liquidation preference per share		$ 1,000	$ 1,000	$ 1,000
Trading day period			20 days
Senior Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Proceeds from issuance of debt		$ 2,200
Minimum [Member] | Depositary Shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			1.85014
Minimum [Member] | Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			37.0028
Maximum [Member] | Depositary Shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			2.17391
Maximum [Member] | Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			43.4782
Subsequent Event [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock, shares issued as stock dividend	3,024,737