Summary of Significant Accounting Policies - Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 25, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Common Stockholders	$ 2,190	$ 1,481	$ 27
Less: Net Income Allocated to Restricted stock awards	$ (12)	$ (8)	$ (5)
Basic Weighted Average Common Shares Outstanding	2,264	2,216	2,230
Basic Earnings Per Common Share	$ 0.96	$ 0.66	$ 0.01
Warrant exercise price				$ 40
Number of warrants expired				293
Unvested restricted stock awards
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities	13	12	10
Warrants to purchase our Class P shares(a)
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities	0	0	116
Convertible trust preferred securities
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities	3	3	3
Mandatory convertible preferred stock(b)
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities	0	48	58
Class P
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Common Stockholders	$ 2,178	$ 1,473	$ 22
Class P | Unvested restricted stock awards
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Awards outstanding	12