Investment Components, Including Associated Derivatives (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	$ 135,375		$ 136,160
Unrealized Gains	1,024		3,267
Unrealized Losses	(1,311)		(423)
Recorded Basis	135,088		139,004
Cash and cash equivalents	9,221	$ 12,859	7,663	$ 6,713	$ 8,468	$ 6,510
Short-term Investments	123,049		125,318
Equity and Other Investments	2,818		6,023
Cash
Cash, Cash Equivalents and Investments [Line Items]
Cash	4,104		3,624
Unrealized Gains	0		0
Unrealized Losses	0		0
Cash and cash equivalents	4,104		3,624
Short-term Investments	0		0
Equity and Other Investments	0		0
Mutual funds
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	683		1,478
Unrealized Gains	0		0
Unrealized Losses	0		0
Recorded Basis	683		1,478
Cash and cash equivalents	683		1,478
Short-term Investments	0		0
Equity and Other Investments	0		0
Commercial paper
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	3,774		319
Unrealized Gains	0		0
Unrealized Losses	0		0
Recorded Basis	3,774		319
Cash and cash equivalents	3,158		69
Short-term Investments	616		250
Equity and Other Investments	0		0
Certificates of deposit
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	2,022		1,358
Unrealized Gains	0		0
Unrealized Losses	0		0
Recorded Basis	2,022		1,358
Cash and cash equivalents	1,156		972
Short-term Investments	866		386
Equity and Other Investments	0		0
U.S. government and agency securities
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	108,056		112,119
Unrealized Gains	31		85
Unrealized Losses	(1,239)		(360)
Recorded Basis	106,848		111,844
Cash and cash equivalents	117		16
Short-term Investments	106,731		111,828
Equity and Other Investments	0		0
Foreign government bonds
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	4,671		5,276
Unrealized Gains	3		2
Unrealized Losses	(12)		(13)
Recorded Basis	4,662		5,265
Cash and cash equivalents	3		1,504
Short-term Investments	4,659		3,761
Equity and Other Investments	0		0
Mortgage- and asset-backed securities
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	3,750		3,921
Unrealized Gains	5		14
Unrealized Losses	(12)		(4)
Recorded Basis	3,743		3,931
Cash and cash equivalents	0		0
Short-term Investments	3,743		3,931
Equity and Other Investments	0		0
Corporate notes and bonds
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	6,139		4,786
Unrealized Gains	27		61
Unrealized Losses	(43)		(12)
Recorded Basis	6,123		4,835
Cash and cash equivalents	0		0
Short-term Investments	6,123		4,835
Equity and Other Investments	0		0
Municipal securities
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	269		284
Unrealized Gains	41		43
Unrealized Losses	(1)		0
Recorded Basis	309		327
Cash and cash equivalents	0		0
Short-term Investments	309		327
Equity and Other Investments	0		0
Common and preferred stock
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	1,324		2,472
Unrealized Gains	917		3,062
Unrealized Losses	(4)		(34)
Recorded Basis	2,237		5,500
Cash and cash equivalents	0		0
Short-term Investments	0		0
Equity and Other Investments	2,237		5,500
Other investments
Cash, Cash Equivalents and Investments [Line Items]
Cost Basis	583		523
Unrealized Gains	0		0
Unrealized Losses	0		0
Recorded Basis	583		523
Cash and cash equivalents	0		0
Short-term Investments	2		0
Equity and Other Investments	$ 581		$ 523