Earnings Per Share - Antidilutive Securities Excluded from Computation of EPS Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income available to common stockholders	$ 268	$ 75
Effect of dilutive securities	36	0
Diluted income per share	$ 304	$ 75
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Weighted average common and common equivalent shares outstanding, basic (in shares)	907	906
Effect of dilutive securities (in shares)	146	1
Weighted average common and common equivalent shares outstanding, diluted (in shares)	1,053	907
Earnings per common share, basic (in dollars per share)	$ 0.30	$ 0.08
Earnings per common share, diluted (in dollars per share)	$ 0.29	$ 0.08
Convertible Preferred Stock [Member]
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Shares of common stock for the following dilutive securities were excluded from the calculation of diluted EPS as the effect was antidilutive:	0	1
Convertible Debt Securities [Member]
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Shares of common stock for the following dilutive securities were excluded from the calculation of diluted EPS as the effect was antidilutive:	0	146
Restricted stock [Member]
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Shares of common stock for the following dilutive securities were excluded from the calculation of diluted EPS as the effect was antidilutive:	0	1
Preferred Stock [Member]
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Shares of common stock for the following dilutive securities were excluded from the calculation of diluted EPS as the effect was antidilutive:	60	60

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise stock options, restrictive stock units (RSUs), convertible preferred stock of an employee stock ownership plan (ESOP), and other dilutive convertible securities.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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