Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value On a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 5,036	$ 5,389
Debt instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	2,664
Debt instruments [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	1,132	652
Debt instruments [Member] | Municipal debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	12	11
Debt instruments [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	914	1,599
Debt instruments [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	329	507
Debt instruments [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	144	169
Debt instruments [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	59	60
Debt instruments [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	5	5
Debt instruments [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	40	43
Debt instruments [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	29	27
Equity instruments [Member] | Fixed income short-term sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	45	44
Equity instruments [Member] | Fixed income U.S. government sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	337	327
Equity instruments [Member] | Fixed income municipal sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	23	22
Equity instruments [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	323	316
Equity instruments [Member] | Fixed income high-yield sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	46	45
Equity instruments [Member] | Fixed income real return sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	285	274
Equity instruments [Member] | Fixed income mortgage sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	533	520
Equity instruments [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	51	50
Equity instruments [Member] | Fixed income emerging market sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	69	66
Equity instruments [Member] | Fixed income international sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	173	171
Equity instruments [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	487	481
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	5,180	3,569
Investments in marketable securities	5,036	5,389
Derivative assets	87	49
Total assets	10,620	10,084
Total liabilities	(3)	(6)
Total net assets	10,617	10,078
Recurring [Member] | Foreign currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1,022	874
Derivative liabilities	(180)	(252)
Recurring [Member] | Interest rate swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	378	361
Derivative liabilities	(454)	(553)
Recurring [Member] | Debt instruments [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	1,132	652
Recurring [Member] | Debt instruments [Member] | Municipal debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	12	11
Recurring [Member] | Debt instruments [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	914	1,599
Recurring [Member] | Debt instruments [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	329	507
Recurring [Member] | Debt instruments [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	144	169
Recurring [Member] | Debt instruments [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	59	60
Recurring [Member] | Debt instruments [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	5	5
Recurring [Member] | Debt instruments [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	40	43
Recurring [Member] | Debt instruments [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	29	27
Recurring [Member] | Equity instruments [Member] | Fixed income short-term sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	45	44
Recurring [Member] | Equity instruments [Member] | Fixed income U.S. government sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	337	327
Recurring [Member] | Equity instruments [Member] | Fixed income municipal sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	23	22
Recurring [Member] | Equity instruments [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	323	316
Recurring [Member] | Equity instruments [Member] | Fixed income high-yield sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	46	45
Recurring [Member] | Equity instruments [Member] | Fixed income real return sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	285	274
Recurring [Member] | Equity instruments [Member] | Fixed income mortgage sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	533	520
Recurring [Member] | Equity instruments [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	51	50
Recurring [Member] | Equity instruments [Member] | Fixed income emerging market sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	69	66
Recurring [Member] | Equity instruments [Member] | Fixed income international sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	173	171
Recurring [Member] | Equity instruments [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	487	481
Recurring [Member] | Money market instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,755	1,424
Restricted Cash Equivalents - money market instruments	317	1,077
Recurring [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,931	1,437
Recurring [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	157	708
Recurring [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	337
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	805	730
Investments in marketable securities	994	879
Derivative assets	0	0
Total assets	2,116	2,686
Total liabilities	0	0
Total net assets	2,116	2,686
Recurring [Member] | Level 1 [Member] | Foreign currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 1 [Member] | Interest rate swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	507	398
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Municipal debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Debt instruments [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income short-term sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income U.S. government sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income municipal sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income high-yield sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income real return sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income mortgage sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income emerging market sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Fixed income international sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 1 [Member] | Equity instruments [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	487	481
Recurring [Member] | Level 1 [Member] | Money market instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	805	730
Restricted Cash Equivalents - money market instruments	317	1,077
Recurring [Member] | Level 1 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 1 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 1 [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,375	2,839
Investments in marketable securities	3,954	4,421
Derivative assets	1,319	1,162
Total assets	9,648	8,422
Total liabilities	(634)	(805)
Total net assets	9,014	7,617
Recurring [Member] | Level 2 [Member] | Foreign currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	944	804
Derivative liabilities	(180)	(252)
Recurring [Member] | Level 2 [Member] | Interest rate swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	375	358
Derivative liabilities	(454)	(553)
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	623	252
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Municipal debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	12	11
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	914	1,599
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	329	507
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	132	157
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	59	60
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 2 [Member] | Debt instruments [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income short-term sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	45	44
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income U.S. government sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	337	327
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income municipal sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	23	22
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	323	316
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income high-yield sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	46	45
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income real return sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	285	274
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income mortgage sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	533	520
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	51	50
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income emerging market sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	69	66
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Fixed income international sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	173	171
Recurring [Member] | Level 2 [Member] | Equity instruments [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 2 [Member] | Money market instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	950	694
Restricted Cash Equivalents - money market instruments	0	0
Recurring [Member] | Level 2 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,931	1,437
Recurring [Member] | Level 2 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	157	708
Recurring [Member] | Level 2 [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	337
Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Investments in marketable securities	88	89
Derivative assets	81	73
Total assets	169	162
Total liabilities	0	0
Total net assets	169	162
Recurring [Member] | Level 3 [Member] | Foreign currency swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	78	70
Derivative liabilities	0	0
Recurring [Member] | Level 3 [Member] | Interest rate swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	3	3
Derivative liabilities	0	0
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	2	2
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Municipal debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Certificates Of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	12	12
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	5	5
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	40	43
Recurring [Member] | Level 3 [Member] | Debt instruments [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	29	27
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income short-term sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income U.S. government sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income municipal sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income high-yield sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income real return sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income mortgage sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income emerging market sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Fixed income international sector fund [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Equity instruments [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	0	0
Recurring [Member] | Level 3 [Member] | Money market instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Restricted Cash Equivalents - money market instruments	0	0
Recurring [Member] | Level 3 [Member] | Certificates of deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 3 [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Recurring [Member] | Level 3 [Member] | U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Recurring [Member] | Counterparty Netting & Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(1,313)	(1,186)
Total assets	(1,313)	(1,186)
Derivative liabilities	631	799
Total liabilities	631	799
Total net assets	$ (682)	$ (387)