Fair Value - Fair Value Measurements on a Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Assets:
Other debt securities	$ 59	$ 51
Deferred purchase price receivable		103
Total assets	431	905
Liabilities:
Contingent consideration	51	46
Total liabilities	51	46
Level 1
Assets:
Other debt securities	0	0
Deferred purchase price receivable		0
Total assets	372	751
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Level 2
Assets:
Other debt securities	56	48
Deferred purchase price receivable		0
Total assets	56	48
Liabilities:
Contingent consideration	0	0
Total liabilities	0	0
Cost basis	40	37
Unrealized gains	16	11
Level 3
Assets:
Other debt securities	3	3
Deferred purchase price receivable		103
Total assets	3	106
Liabilities:
Contingent consideration	51	46
Total liabilities	51	46
Money market funds and money market deposit accounts
Assets:
Cash and cash equivalents	5	156
Money market funds and money market deposit accounts | Level 1
Assets:
Cash and cash equivalents	5	156
Money market funds and money market deposit accounts | Level 2
Assets:
Cash and cash equivalents	0	0
Money market funds and money market deposit accounts | Level 3
Assets:
Cash and cash equivalents	0	0
Time deposits
Assets:
Cash and cash equivalents	367	595
Time deposits | Level 1
Assets:
Cash and cash equivalents	367	595
Time deposits | Level 2
Assets:
Cash and cash equivalents	0	0
Time deposits | Level 3
Assets:
Cash and cash equivalents	$ 0	$ 0