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Preferred and Common Stock - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 | Mar. 31, 2014
Class of Stock [Line Items] |  |  |  |  |
Transaction date of public offering |  |  | Jul. 30, 2014 |  |
Public offering of preferred stock |  |  | $ 1,250 |  |
Depository shares |  |  | 25,000,000 |  |
Interest in preferred stock | 0.1 |  | 0.1 |  |
Proceeds from public offering |  |  | $ 1,213 |  |
Preferred stock dividend declared | $ 0.09375 | $ 1.875 | $ 2.8125 | $ 3.75 |
Common stock shares, issued | 1,267,290,820 |  | 1,267,290,820 |  |
Common stock shares, Authorized |  |  |  |  | 1,800,000,000
Common stock shares, outstanding | 1,177,672,033 |  | 1,177,672,033 |  |
5.25% Convertible Notes Due March 15, 2014 [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Common stock shares, issued |  |  |  |  | 89
Common stock shares |  |  |  |  | $ 1
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 5.25%
IPO [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Underwriter 30-day common stock options |  |  | 30 days |  |
IPO [Member] | Depository Shares [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Additional shares granted |  |  | 3,750,000 |  |
Maximum [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock conversion price | $ 30.9406 |  | $ 30.9406 |  |
Minimum [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock conversion price | $ 25.7838 |  | $ 25.7838 |  |
Class B Mandatory Convertible Preferred Stock [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Percentage ownership |  |  | 5.375% |  |
Preferred stock issued | 10,000,000 |  | 10,000,000 |  |
Mandatory Convertible Preferred Stock [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock par value | $ 1 |  | $ 1 |  |
Preferred stock liquidation preference | $ 500 |  | $ 500 |  |
Preferred share | 2,500,000 |  | 2,500,000 |  |
Preferred stock dividend declared |  |  | $ 26.8750 |  |
Percentage redemption of preferred shares |  |  | 101.00% |  |
Termination date of preferred stock |  |  | Apr. 01, 2015 |  |
Preferred stock conversion date |  |  | Oct. 01, 2017 |  |
Mandatory Convertible Preferred Stock [Member] | IPO [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Additional shares granted |  |  | 375,000 |  |
Mandatory Convertible Preferred Stock [Member] | Maximum [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock conversion price | $ 30.9406 |  | $ 30.9406 |  |
Mandatory Convertible Preferred Stock [Member] | Minimum [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock conversion price | $ 25.2994 |  | $ 25.2994 |  |
Mandatory Convertible Preferred Stock [Member] | Minimum [Member] | Anti - Dilution Adjustments [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Preferred stock conversion price | $ 25.7838 |  | $ 25.7838 |  |

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