Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value On a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	$ 6,128
Available-for-sale securities total	8,241	$ 7,131
Derivative assets	53	53
Counterparty netting and collateral	(120)	(145)
Derivative liabilities	(75)	(90)
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	368	145
U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	4,118	4,359
Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	11	12
U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	50	59
Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	3	4
Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	42	44
Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	36	39
Fixed income short-term floating NAV fund II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	180	148
Fixed income U.S. government sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	255	335
Fixed income municipal sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	19	20
Investment Grade Corporate Sector Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	244	268
Fixed income high-yield sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	101	55
Fixed income real return sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	221	232
Fixed income mortgage sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	327	399
Fixed income asset-backed securities sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	124	72
Fixed income emerging market sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	95	71
Fixed income international sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	145	160
Fixed income short-term sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		37
Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	2,592	2,214
Available-for-sale securities total	8,241	7,131
Derivative assets	53	53
Assets at fair value	10,886	9,398
Liabilities at fair value	(75)	(90)
Net assets at fair value	10,811	9,308
Recurring [Member] | Money market instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,566	1,069
Recurring [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,000	1,105
Available-for-sale securities, Debt instruments	1,325	175
Recurring [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	175	37
Recurring [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		40
Recurring [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	26
Available-for-sale securities, Debt instruments	368	145
Recurring [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	4,118	4,359
Recurring [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	11	12
Recurring [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	50	59
Recurring [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	3	4
Recurring [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	42	44
Recurring [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	36	39
Recurring [Member] | Fixed income short-term floating NAV fund II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	180	148
Recurring [Member] | Fixed income U.S. government sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	255	335
Recurring [Member] | Fixed income municipal sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	19	20
Recurring [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	244	268
Recurring [Member] | Fixed income high-yield sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	101	55
Recurring [Member] | Fixed income real return sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	221	232
Recurring [Member] | Fixed income mortgage sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	327	399
Recurring [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	124	72
Recurring [Member] | Fixed income emerging market sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	95	71
Recurring [Member] | Fixed income international sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	145	160
Recurring [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	402	460
Recurring [Member] | Fixed income short-term sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		37
Recurring [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	163	217
Derivative liabilities	(1,871)	(1,888)
Recurring [Member] | Interest rate swap [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	423	471
Derivative liabilities	(235)	(386)
Recurring [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	958	289
Available-for-sale securities total	5,165	4,712
Derivative assets	0	0
Assets at fair value	6,123	5,001
Derivative liabilities	0	0
Liabilities at fair value	0	0
Net assets at fair value	6,123	5,001
Recurring [Member] | Level 1 [Member] | Money market instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	958	249
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
Available-for-sale securities, Debt instruments	675	0
Recurring [Member] | Level 1 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	37
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		40
Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	27	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]
Available-for-sale securities, Debt instruments	4,061	4,215
Recurring [Member] | Level 1 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 1 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 1 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 1 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 1 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income short-term floating NAV fund II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income U.S. government sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income municipal sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income high-yield sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income real return sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income mortgage sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income emerging market sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Fixed income international sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 1 [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	402	460
Recurring [Member] | Level 1 [Member] | Fixed income short-term sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		0
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
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
Derivative liabilities	0	0
Recurring [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,634	1,925
Available-for-sale securities total	2,985	2,316
Derivative assets	585	680
Assets at fair value	5,204	4,921
Derivative liabilities	0	0
Liabilities at fair value	(2,100)	(2,274)
Net assets at fair value	3,104	2,647
Recurring [Member] | Level 2 [Member] | Money market instruments [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	608	820
Recurring [Member] | Level 2 [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,000	1,105
Available-for-sale securities, Debt instruments	650	175
Recurring [Member] | Level 2 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	175	0
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		0
Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	26
Available-for-sale securities, Debt instruments	333	131
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]
Available-for-sale securities, Debt instruments	55	142
Recurring [Member] | Level 2 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	11	12
Recurring [Member] | Level 2 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	50	59
Recurring [Member] | Level 2 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 2 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 2 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 2 [Member] | Fixed income short-term floating NAV fund II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	180	148
Recurring [Member] | Level 2 [Member] | Fixed income U.S. government sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	255	335
Recurring [Member] | Level 2 [Member] | Fixed income municipal sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	19	20
Recurring [Member] | Level 2 [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	244	268
Recurring [Member] | Level 2 [Member] | Fixed income high-yield sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	101	55
Recurring [Member] | Level 2 [Member] | Fixed income real return sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	221	232
Recurring [Member] | Level 2 [Member] | Fixed income mortgage sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	327	399
Recurring [Member] | Level 2 [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	124	72
Recurring [Member] | Level 2 [Member] | Fixed income emerging market sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	95	71
Recurring [Member] | Level 2 [Member] | Fixed income international sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	145	160
Recurring [Member] | Level 2 [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 2 [Member] | Fixed income short-term sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		37
Recurring [Member] | Level 2 [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	163	210
Derivative liabilities	(1,868)	(1,888)
Recurring [Member] | Level 2 [Member] | Interest rate swap [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	422	470
Derivative liabilities	(232)	(386)
Recurring [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Available-for-sale securities total	91	103
Derivative assets	1	8
Assets at fair value	92	111
Derivative liabilities	0	0
Liabilities at fair value	(6)	0
Net assets at fair value	86	111
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
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
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 3 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	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] | Level 3 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	8	14
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]
Available-for-sale securities, Debt instruments	2	2
Recurring [Member] | Level 3 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 3 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	0	0
Recurring [Member] | Level 3 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	3	4
Recurring [Member] | Level 3 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	42	44
Recurring [Member] | Level 3 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt instruments	36	39
Recurring [Member] | Level 3 [Member] | Fixed income short-term floating NAV fund II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income U.S. government sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income municipal sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Investment Grade Corporate Sector Fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income high-yield sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income real return sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income mortgage sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income asset-backed securities sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income emerging market sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		0
Recurring [Member] | Level 3 [Member] | Fixed income international sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Equity mutual fund - S&P 500 index [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments	0	0
Recurring [Member] | Level 3 [Member] | Fixed income short-term sector fund [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Equity instruments		0
Recurring [Member] | Level 3 [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	7
Derivative liabilities	(3)	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	1	1
Derivative liabilities	(3)	0
Recurring [Member] | Counterparty Netting & Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	(533)	(635)
Counterparty netting and collateral	(533)	(635)
Assets at fair value	(533)	(635)
Derivative liabilities	2,031	2,184
Liabilities at fair value	2,031	2,184
Net assets at fair value	$ 1,498	$ 1,549