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Summary of Significant Accounting Policies - Early Adoption (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Mar. 31, 2018 | Jan. 01, 2018 | Dec. 31, 2017
--- | --- | --- | --- | ---
Disaggregation of Revenue [Line Items] |  |  |  |
Net receivables | $ 4,317 |  | $ 4,201 | $ 4,133
Other current assets | 551 |  | 542 | 224
Other assets | 1,539 |  | 1,656 | 1,430
Deferred tax assets |  |  | 552 | 669
Accounts payable and accrued liabilities | 2,234 |  | 2,205 | 2,083
Other liabilities | 1,362 |  | 1,334 | 1,311
Other Accumulated Comprehensive Income |  |  | (14) | 0
Retained earnings | 14,347 |  | 13,504 | $ 13,140
Accounting Standards Update 2014-09 |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net receivables | 4,317 |  | 68 |
Other current assets | 551 |  | 318 |
Other assets | 1,539 |  | 226 |
Deferred tax assets | 680 |  | (103) |
Accounts payable and accrued liabilities | 2,234 |  | 122 |
Other liabilities | $ 1,362 |  | 23 |
Other Accumulated Comprehensive Income |  |  | 0 |
Retained earnings |  | $ 364 | 364 |
Accounting Standards Update 2016-01 |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net receivables |  |  | 0 |
Other current assets |  |  | 0 |
Other assets |  |  | 0 |
Deferred tax assets |  |  | 0 |
Accounts payable and accrued liabilities |  |  | 0 |
Other liabilities |  |  | 0 |
Other Accumulated Comprehensive Income |  |  | (14) |
Retained earnings |  |  | 14 |
Accounting Standards Update 2016-16 |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Net receivables |  |  | 0 |
Other current assets |  |  | 0 |
Other assets |  |  | 0 |
Deferred tax assets |  |  | (14) |
Accounts payable and accrued liabilities |  |  | 0 |
Other liabilities |  |  | 0 |
Other Accumulated Comprehensive Income |  |  | 0 |
Retained earnings |  |  | $ (14) |

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