Income Taxes - Reconciliation of unrecognized tax benefits (UTB) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Federal, State and Foreign Tax | |||
| Gross UTB Balance at January 1 | $ 319 | $ 381 | $ 583 |
| Additions based on tax positions related to the current year | 119 | 67 | 77 |
| Additions for tax positions of prior years | 149 | 43 | 140 |
| Reductions for tax positions of prior years | (38) | (66) | (399) |
| Settlements (UTB decreases) | (3) | (95) | (4) |
| Reductions due to lapse of applicable statute of limitations | (16) | (11) | (16) |
| Gross UTB Balance at December 31 | $ 530 | $ 319 | $ 381 |
| X | ||||||||||
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. No definition available.
|
| X | ||||||||||
- Definition Amount of unrecognized tax benefits. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|