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Condensed Financial Information (Parent Company) (Long-term Debt Outstanding) (Details) - Parent Company $ in Millions, ¥ in Billions | Dec. 31, 2023 USD ($) | Jul. 10, 2023 JPY (¥) | Jul. 08, 2023 JPY (¥) | Mar. 31, 2023 | Dec. 31, 2022 USD ($) | Mar. 31, 2022 | Dec. 31, 2021 | Dec. 16, 2021 JPY (¥) | Jul. 15, 2021 JPY (¥)
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Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  | 124.00% | 5.23% | 100.00% | 212.00% |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes | $ | $ 14,516 |  |  |  | $ 13,588 |  |  |  |
Long-term Debt | $ | 16,101 |  |  |  | 15,264 |  |  |  |
Senior Notes, Unaffiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes | $ | 14,516 |  |  |  | 13,588 |  |  |  |
Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes | $ | $ 1,585 |  |  |  | $ 1,676 |  |  |  |
Minimum | Senior Notes, Unaffiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 0.50% |  |  |  |  |  |  |  |
Minimum | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 1.59% |  |  |  |  |  |  |  |
Maximum | Senior Notes, Unaffiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 6.50% |  |  |  |  |  |  |  |
Maximum | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 7.49% |  |  |  |  |  |  |  |
SeniorDebtYen53.7BillionJune2021 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 2.9725%
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  | ¥ 53.7
SeniorDebtYen13.7BillionJuly2026 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 1.61%
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  | ¥ 13.7
SeniorDebtYen14.3BillionJuly2028 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 1.755%
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  | ¥ 14.3
SeninorDebtYen25.7BillionJuly2031 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  |  | ¥ 25.7
SeniorDebtYen25.7BillionJuly2028 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 1.852%
SeniorDebtYen54.6BillionDecember2021 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 3.135% |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  | ¥ 54.6 |
SeniorDebtYen12.2BillionDecember2021 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 1.588% |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  | ¥ 12.2 |
SeniorDebtYen19.1BillionDecember2021 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 1.7185% |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  | ¥ 19.1 |
SeniorDebtYen23.3BillionDecember2021 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  | 1.85% |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  |  |  |  |  |  | ¥ 23.3 |
SeniorDebtYen37.3BillionJuly2023 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 1.6015% |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  |  | ¥ 37.3 |  |  |  |  |  |
SeniorDebtYen37.3BillionJuly2030 | Senior Notes, Affiliated [Member] |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 2.1575% |  |  |  |  |  |  |
Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |
Senior Notes |  | ¥ 37.3 |  |  |  |  |  |  |
Note $80M 5.68% maturity March 2033 |  |  |  |  |  |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 5.68% |  |  |  |  |  |  |  |

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